"The One Where Monica Sings" is the thirteenth episode of season nine of Friends. It aired on January 30, 2003.
Phoebe convinces Monica to come to Mike's karaoke night at a bar, but tells her she doesn't have to sing. However, she gets Monica to change her mind who starts to sing and is appluaded by the mostly male audience because you can see through her shirt. Chandler arrives later on and notices it and tries to get her to stop, but she decides to continue anyway.
Ross tells Chandler about him seeing Rachel kiss Gavin on the balcony after the party and says if she wants to move on then so will he. He goes to Central Perk to attempt to pick up girls failing drastically. Meanwhile, Gavin comes over to talk to Rachel about the situation with Ross, Rachel says it's fine but makes him hide when she hears someone entering the apartment (which turns out to be Emma's nanny, Molly) which shows to Gavin that there is something wrong. He tells Rachel to talk to Ross. Meanwhile, a woman named Michelle enters the coffeehouse crying for a recent breakup, Ross makes his move and brings her to his apartment. Rachel comes back in and finds Ross and Michelle already feels a connection. Ross admits it was a rebound after she leaves after saying he saw Rachel kiss Gavin. She says it was a one time thing but Ross reveals about how she gave her number to a man at the bar. Ross tells how he called her and he put the message in his back pocket, frustrating Rachel for hiding her messages. She moves out and goes back to live with Joey.
Meanwhile, Joey gets his eyebrows waxed but it hurts after the first one is plucked so he leaves. Chandler does the other one for him after revealing how he'd get his allowance by plucking the eyebrows out of his dad and co-workers ahead of performances.