The One Where Nana Dies Twice - S1-E8
Corrected entry: Rachel says to Chandler that she thought he was gay when she first met him, but then later he spent "Phoebe's entire birthday party staring at her breasts". In a later season, we find out that they kissed when Chandler was in college and Rachel in high school. Also. Phoebe has not had a birthday since Rachel and she met for the first time.
Correction: I used to work with an openly gay man who slept with more women in high school and college than I, or most of my friends, did. Chandler and Rachel kissing is in no way an indication of whether he was gay or not.
rswarrior