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"
Kristen Stewart, Paula Abdul, and Kim Kardashian all get an F on this week's Fashion Offenders.
"Shah's of Sunset" star Asa Soltan talks about this season's drama, possible wedding bells with her boyfriend and more.
Victoria’s Secret Angel Candice Swanepoel talks to WW about wearing the $10 million bra, eating steak, Taylor Swift and if she plans to marry her boyfriend.
Find out why Lena Dunham, Jaden Smith, and Rihanna need fashion resolutions for 2014.
From Jenny and Donnie to Amanda and Justin, see more celebs who found new love in 2013.
From Olivia Wilde to Mario Lopez, see which stars have the hottest beach bods of 2013.
© 2013 Microsoft