4x07 "The One Where Chandler Crosses the Line"

Chandler must decide between the girl of his dreams, Kathy, and his best friend Joey when he and Kathy share a secret and secluded passionate kiss. Chandler, feeling guilty about his kiss with Kathy, buys new furniture and appliances for his and Joey's apartment to fill in the empty spaces left after the robbery. When Joey finds out about the kiss, he attempts to punish Chandler for five years. Ross starts playing the keyboard again for the first time since college and reinvents his musical art (or as Ross calls them, "wordless sound poems").