Don't hold back, Elisabeth Moss! During "Plead the Fifth" on Andy Cohen's Watch What Happens Live Thursday, May 23, the Mad Men actress sounded off on her 2008 Speed-the-Plow costar Jeremy Piven.
"What, besides eating too much sushi, caused Jeremy Piven to quit Speed-the-Plow?" Cohen asked the actress. (Piven, 47, famously left the Broadway production early, claiming he had mercury poisoning.)
PHOTOS: Biggest celebrity feuds
"That's a very good one. I could go on and on," Moss, 30, said, with a big smile on her face. "Being highly unprofessional," she gave as her answer.
"We were all surprised," Moss added of Piven's exit. "It came out of nowhere. He just didn't come back one day."
PHOTOS: Stars on set
But she did run into him not long after he left. "I saw him like a month later at the Golden Globes," she shared. "When he was supposed to be really sick."
PHOTOS: Mad Men cast -- see how they look off-camera
Cohen also asked Moss about the rumors that her Mad Men costar, Jon Hamm, has "impressive anatomy." "Is it true what they say about Jon Hamm's ham?" he asked.
"Well, I mean, we've all seen the pictures so, I mean, I would suppose so," Moss said with a smirk. "That's all I know."
This article originally appeared on Usmagazine.com: Elisabeth Moss Slams Jeremy Piven as "Highly Unprofessional"
Joe Manganiello parties with new love Sofia Vergara and her family in Miami on today's Celebs Gone Social.
It's been 20 years since "Jurassic Park" came out. See what the cast of the movie is up to these days.
Check out some of January Jones' most retro wardrobe choices from over the years.
Selena Gomez, Zoe Saldana, and Maggie Gyllenhaal all get an F on this week's Fashion Offenders.
Get the scoop on Naya Rivera's wacky wedding on Replay hosted by Wonderwall's Kirby Kristen.
Find out which stars attended Jennifer Lopez's birthday celebration on today's Celebs Gone Social.
© 2014 Microsoft