A lot of famous faces appeared on Friends over the years, from George Clooney to Charlie Sheen and Bruce Willis, all of which have gone down a hit with fans.
However, there was one in particular who Lisa Kudrow, who of course played Phoebe Buffay, was not too fond of.
When asked about the worst behaviour on set in an interview on Watch What Happens Live with Andy Cohen (via E! Online), Kudrow said: "The worst behaviour, off the top of my head?"
Going on to tell the host: "I rehearsed without make-up most of the week, and then on show night, I'm in hair and make-up, and I was told, 'Oh wow, now you're f**kable'.
"That's bad behaviour, I say."
When asked what happened next, Lisa said: "I told Matt LeBlanc," she said. "He's like a big brother."
The actress refused to say who the guest star was but confirmed it definitely wasn't Charlie Sheen, who played her boyfriend Ryan in the episode 'The One with the Chicken Pox'.
Probably like you, we are now racking our brains trying to work out who could have said such a downright disgusting comment... Ben Stiller? No, hardly. Sean Penn??
Please just say it wasn't Jon Favreau...