Leonard and Penny have a fight when she tells him that a former boyfriend and musician will be sleeping over on her couch while he's in California. Sheldon gets upset when they fight and runs away. Leonard and Penny treat him like their own child.
Sheldon invented his own board game: Research Lab ("The Physics is Theoretical, But the Fun is Real!") Sheldon is using Penny and Leonard as beta testers playing the game with him. They quit because Penny has to pick up her friend Justin from the airport. Justin plays the guitar and has a lot of stuff. Penny mentions that he will be crashing on her couch for a couple of weeks while he finds some recording studio time. Leonard is shocked and wonders how close of a friend he is. Penny says she and him went out once or twice, but were never serious. Leonard, her boyfriend, doesn't like him in her apartment. Sheldon wants to get back to the game. As their fight heats up, Sheldon gets upset and goes over to the kitchen and turns on the sno-cone maker to drown out the fight. Penny gives up trying to talk over the blender and leaves, while Leonard has won the first game of "Research Lab," and a celebratory sno-cone.
Leonard is still complaining about Penny in his car on the way to work. Sheldon doesn't appear to be getting used to people fighting. Leonard keeps complaining, causing Sheldon to jump out of the car and walk.
With only seventeen minutes for guys to get to the movies, they run into Penny, who hopes Leonard is ready to apologize. Leonard doesn't and Penny again reads him the riot act in front of Howard and Raj. Sheldon leaves.
Killing time before the next showing, they go to the comic book store. Howard agrees that Penny was out of line, but she'll probably have a new boyfriend by this time tomorrow. Leonard will have to build a new girlfriend. Raj thinks Leonard is wrong. He tells about the time he took a cooking class with Howard, but Howard blew him off to do a liquid cleansing diet with his mother. They start arguing about his mother which freaks Sheldon out.
SHELDON: STOP IT, BOTH OF YOU! ALL THIS FIGHTING, I MIGHT AS WELL BE BACK WITH MY PARENTS!! "DAMN IT, GEORGE, I TOLD YOU IF YOU DIDN'T QUIT DRINKING I'D LEAVE YOU!" "WELL, I GUESS THAT MAKES YOU A LIAR. CAUSE I'M DRUNK AS HELL AND YOU'RE STILL HERE!" "STOP YELLING! YOU'RE MAKING SHELDON CRY!" "I'LL TELL YOU WHAT'S MAKING SHELDON CRY! THAT I LET YOU NAME HIM SHELDON!"
Sheldon goes to the Cheesecake Factory supposedly to have lunch to ask Penny to apologize to Leonard, but she refuses. Sheldon mentions several complaints Leonard has about her, which he was too much of a gentleman to confront her about: her driving, the bed full of stuffed animals that stare at him during their "amorous activities," her tardiness, or her singing. This revelation ticks Penny off even more. Her message to Leonard is that he can drop dead! Sheldon then comments, sotto voce, about how Penny's attitude toward her job, and her obliviousness to same, keeps her from getting bigger tips.
Sheldon quickly goes home and suggests to Leonard to apologize to Penny before she gets back. Penny comes storming in at full boil to yell at Leonard over the list that Sheldon detailed to her. While Leonard stands up to Penny and criticizes her for her hypocrisy, Sheldon again runs away and goes to Raj’s apartment. He is having a fight with his parents over coming to New Delhi for Cousin Sanjay's wedding. Sheldon again runs away.
After driving around, Leonard and Penny find Sheldon at the comic book store where he made a nest according to Stuart. Leonard describes how he pretends to be in an alternate universe where Leonard and Penny don't exist. Sheldon comments that he shouldn't flatter himself because he is just ignoring them. Leonard and Penny try to convince him they're done fighting.
SHELDON: I've heard that before. The next thing you know I'm in my bedroom blaring a Richard Feynman lecture while my mother is shouting that Jesus would forgive her for putting ground glass in my father's meat loaf. And my dad is on the roof skeet-shooting her Franklin Mint collectible plates.
Leonard and Penny still haven’t resolved the Justin issue, though Penny tells Sheldon that in a relationship and people sometimes fight, but that they will always love him. Still sounding like Sheldon’s parents they buy him a toy robot and a comic book so that he will come home. Leonard, sounding like his father, complains that he'll just play with it twice and it will end up in his closet.
Finally while Leonard and Penny have mended their relationship, Justin is asleep on Leonard’s couch right next to Sheldon, prompting Sheldon to say "I should have asked for much more than a comic book and a robot."
- Guest starring:
- Teleplay: Bill Prady, Richard Rosenstock & Jim Reynolds
- Story: Chuck Lorre & Lee Aronsohn
- "The show remains tantalizingly close to producing really good TV, but forever sell themselves short at the altar of the lame punch line." - The TV Critic's Review
- IMDb user reviews
- Title Reference: Penny's visiting friend's occupation as a professional guitar player.
- Chuck Lorre's vanity card 
- This episode was watched by 12.79 million people with a rating of 4.7 (18-49).
- This episode aired in Canada on November 9, 2009.
- Episode transcript 
- The actor who appears at the end as Penny's guitarist friend, who is crashed out on the couch in Leonard and Sheldon's apartment, is not credited in the episode, neither is he listed in the episode's cast listing at IMDb.
- This episode, the previous episode (S3E6) and the next episode (S3E8) feature no guest appearances by Melissa Rauch as Bernadette until "The Vengeance Formulation" (S3E9).
- When Penny leaves the table that Sheldon sits at in the Cheesecake Factory, there is no coming up to the table appearance by Bernadette as the Cheesecake Factory waitress or any other waitress at the Cheesecake Factory to ask what Sheldon would like to eat or drink before she writes it down in her notebook. Bernadette and her Cheesecake Factory waitress shift aren't seen until "The Vengeance Formulation" (S3E9).
- Raj, Leonard and Howard are not featured in the Cheesecake Factory scene with Sheldon because he (Sheldon) is personally setting up excuses for Penny to "apologize for Leonard" himself.
- Sheldon talks about "blaring a Feynman lecture." Richard Feynman has also been mentioned in "The Peanut Reaction", "The Zazzy Substitution", "The Vacation Solution" and "The Werewolf Transformation".
- Sheldon makes a sno-cone without The Original Snoopy Snow-Cone Machine seen later in "The Irish Pub Formulation" (S4E06).
- Penny whistles for Sheldon when he disappears from the apartment, with Leonard proclaiming he is not a lost dog. Similarly, in "The 21-Second Excitation", Raj whistles to summon a missing Sheldon from an unattended projection booth at a theater, to which Howard remarks, "We're looking for Sheldon, not Marmaduke." The whistling does work on Sheldon.
- Sheldon mentions that Penny moved in three years ago, However, since this episode takes place in 2009, That would mean she moved in the apartment during 2006. It has actually been two years since Penny moved in which was in 2007 in the Pilot.
- (The adults are arguing in the apartment)
- (Sheldon turns on the blender)
- Penny: WHAT THE HELL IS HE DOING?!
- Leonard: He's drowning us out; he doesn't like fighting!
- (The Guys are in the hero store while Howard and Raj are starting to argue to Leonard about who was to blame in Leonard's and Penny's argument about Justin.)
- Raj (To Leonard): It's like my girl Beyoncé says: "If you like it, then you should've put a ring on it."
- (Leonard looks confused)
- Howard: Oh, come on, at the very least when she found out Leonard was upset about it, she should've backed off.
- Raj: You mean like when a guy is upset because his friend agreed to go to cooking class with him and then doesn't show up because he was doing a juice fast with his mother?
- Howard: I didn't know you were upset about that.
- Raj: Really? Did you miss all the subtle indicators like me saying, "Howard, I am upset!"?
- (Sheldon notices them fighting.)
- Howard: OKAY! Sorry.
- Raj: Maybe it must mean something different in this country, but back in India, it means you are upset with a guy named Howard!
- Howard: OKAY! I said I'm sorry.
- Raj: Sorry doesn't make it up to the fact that I had to make Chicken and Rice with this vegan guy, You know what vegan chicken with rice is? RICE!
- Howard: NAH, WELL DID YOU THINK I WAS HAVING FUN SITTING AROUND ALL NIGHT LISTENING TO MY MOTHER SAYING TO ME (imitating Mrs. Wolowitz) "HAVE YOU EVER PEED SO MUCH IN YO LIFE?!"?!
- (Sheldon is getting upset and stressed by Howard and Raj's fight.)
- Raj: OH..., MY... GOD, YOU ARE SUCH A MAMA'S BOY!
- Howard: HEY, DON'T BRING MY MOTHER INTO THIS!
- Raj: YOU BROUGHT YOUR MOTHER INTO THIS!
- (Sheldon finally loses his temper at them.)
- Sheldon: STOP IT, BOTH OF YOU, All this fighting; I might as well be back with my parents!
- (imitating mother) Damn it, George; I told you if you didn't quit drinking, I'd leave you!
- (imitating father) Well, I guess that makes you a liar, 'cause I'm drunk as hell and you're still here!
- (imitating mother) Stop yelling! You're making Sheldon cry!
- (imitating father) I'll tell you what's making Sheldon cry, that I let you name him Sheldon!
- (Sheldon storms out of the store and everyone is dazzled.)
- Howard: Boy, what got him so upset?
- Raj: Oh, sure, you can tell when Sheldon's upset.
- (Sheldon has run away from Leonard and Penny and has gone to Howard's house. He is about to knock)
- Mrs Wolowitz: HOWAAAHD, ANSWER THE DOOAH, I'M BUSY!
- Howard: I'M BUSY TOO, YOU ANSWER IT!
- Mrs Wolowitz: I CAN'T, I'M ON THE TOILET!
- Howard: FOR GOD'S SAKES, I DON'T HAVE TO HEAR THAT! CAN'T YOU JUST SAY "I'M BUSY"?!
- Mrs Wolowitz: I SAID I'M BUSY, BUT THAT WASN'T GOOD ENOUGH FOR YOU!
- (The camera pulls close to the door and Sheldon starts to leave.)
- Howard: YOU KNOW WHAT, I HOPE IT'S ONE OF THOSE HOME INVASION DEALS AND THEY SHOOT ME IN THE HEAD!
- Mrs Wolowitz: WELL, IF IT'S HOME INVADERS, DON'T TELL THEM I'M ON THE TOILET!
- (When Howard opens the door, he finds no one there and had realized he had been knock-knock ditched.)
- Howard: THERE'S NO ONE THERE, YOU'RE HEARING THINGS, CRAZY OL' LADY!