Friends Season 5 Episode 8 : The One With The Thanksgiving Flashbacks (a.k.a. The One With All The Thanksgivings)
It's Thanksgiving, and everybody has flashbacks of their worst thanksgiving. Phoebe recalls her Thanksgiving in 1862, which happened in one of her "past lives". Rachel reveals Monica's worst Thanksgiving, at which Monica accidentally cut off Chandler's little toe. When Monica tries to get Chandler to forgive her, he accidentally reveals that he's in love with her and quickly tries to retract it.