Tim and Tomas are played by Billy Crystal and Robin Williams respectively. The cameo was actually not originally written for the episode, as the two actors were doing something nearby and were asked if they wanted to make an appearance on the sitcom Friends. So it was mostly improv.

They play two friends who share the couch with the cast and have a very loud conversation, which they overhear quite easily.

Robin Williams’ character Tomas notices that his wife is cheating on him and Billy Crystal’s character Tim admits that it was him.

Leaving the main cast of Friends utterly speechless. I bet the first time they did that take they probably could not stop themselves from laughing.