"The One With The Tiny T-Shirt" is the nineteenth episode of the third season of Friends, wich aired in March 27, 1997.
Monica and Pete are going out together. Monica thinks Pete is great, except for one thing - she's not sexually attracted to him in any way. She can't even bring herself to kiss him (except on the cheek), but instead touches him with friendly moves like tousles and pats. Pete finally confronts her, and Monica admits the non-attractiveness she feels towards him. However, Pete is willing to stand this.
Joey gets the part in a play he's been hoping to get. Unfortunately for him, things don't start off too well with his co-actor Katie, who recognizes him from the MilkMaster informercial (from The One With The Metaphorical Tunnel) and ridicules him with the others by making them ask him to open their milk cartons. Joey can't stand the woman, but Chandler really thinks that Joey has a crush on her and that the ridicule she's making him face just makes her a hard-to-get girl for him. Joey denies this, but he works up his feelings and decides to ask her out, when the play director comes and takes Katie away - Joey then realizes that Katie is the director's girlfriend.
Mark meets Rachel at the coffeehouse and reveals that he's had a crush on her and that now that she's not with Ross anymore, he'd like to ask her out. Rachel ponders this but decides not to accept as she feels she would be cheating with Ross if she accepted. She calls Ross over to give him a box of his stuff, helping him "move on". Ross acts out on this, and asks for a lot more of his stuff, including the tiny T-shirt she sleeps in. Out of spite, Ross wears the T-shirt he hasn't worn since he was 15 and leaves her apartment in it. When he sees Rachel leave the apartment the next time, she's leaving with Mark. Ross then stays in Chandler and Joey's apartment, waiting for Rachel and Mark to come back. He watches through the peephole for several hours until they finally arrive. Rachel lets Mark into her apartment, which makes Ross insane. He tries to make up a reason to go into Rachel's apartment, hoping to stop whatever Rachel and Mark may be doing. He comes up with the idea of borrowing juice from Rachel, which could've been a legitimate reason until Chandler tries to stop him at all cost. He physically stops Ross, letting him realize that the Ross-Rachel relationship is truly over and that, in some way or another, he must find a way to move on. In the meantime, Rachel realizes she's just dating Mark to get back at Ross, while Mark suggests getting back at Ross on the couch, but Rachel rejects. Mark says it's okay and says he'd go home and 'get back at him by himself'. Some time later, Ross gives Rachel a box of her stuff - which includes the tiny T-shirt she loves so much.