Season 5: Episode 109: The One With Chandler's Work Laugh
Monica attends one of Chandler's work parties, where she is exposed to his fake work laugh. Laughing at his bosses lame jokes, Chandler insists that it's just something he has to do. The two then play a tennis game with Chandler's boss and his wife, bringing out the ultra-competitive side of Monica. After pummeling their opponents in the first games, Chandler asks Monica to let his boss win a game. Monica refuses, so Chandler must make an effort to lose the game. When he succeeds, his boss invites he and Monica over for dinner. Once again Chandler fake laughs at all his bosses jokes, until Monica tells him that she can't stand seeing him this way. Chandler finally stands up to his boss and doesn't laugh at his joke, which greatly upsets his boss. Realizing he's in trouble, Monica jumps in and "explains" the joke to Chandler, then they both fake laugh for his bosses benefit. Meanwhile, Rachel tries to get Monica to admit her romance with Chandler. But Monica continues to lie to her in an effort to keep the relationship a secret. Frustrated, Rachel finally goes over to Chandler's apartment to confront them, and overhears Monica telling Chandler how difficult it is to keep lying to Rachel, since she's her best friend. Touched by what she's overheard, Rachel decides to leave quietly, but accidentally trips over a cord and knocks a lamp over on her way out. Monica comes out of Chandler's room and sees Rachel, then both women make up lies to conceal what they're really doing there. Rachel' pretends she doesn't know that anything's going on, and Monica pretends that she's there cleaning.