The 10 Strangest Celeb Guest Spots on 'Friends' Ever

Friends ran on NBC from 1994-2004, and during its 10 seasons the show produced its fair share of celebrity cameos. Although everyone remembers Brad Pitt's appearance in the classic Thanksgiving episode 'The One with the Rumor,' you may have missed these other celebs who stopped by in bizarre plot lines. Pull up a seat on the big, orange couch and see for yourself!

Sean Penn (Season 8) 'The One with the Halloween Party'

Two-time Academy Award winner Sean Penn guest starred in two season eight episodes back in 2001 playing Ursula Buffay's fiancée. When the gang throws a Halloween party, Phoebe's identical twin sister shows up with her new fiancée Eric, but it doesn't take long for Phoebe to realize that Ursula has been lying about herself to her soon-to-be husband. When Phoebe sets the record straight, Eric dumps Ursula and starts dating Phoebe. Unfortunately, Eric can't handle Phoebe's obvious resemblance to her twin sister -- both played by Lisa Kudrow -- and their romance is cut short.