"The very first day of rehearsal, he shoved his tongue all the way down to my heart," Messing told Andy Cohen on "Watch What Happens: Live" this week. "I was just like, 'Whoa!' ... Every time, he went for it."
Piven appeared on the show in 2000 as Grace's former boyfriend, who asks her to join him and his current girlfriend for a threesome. Messing says that, thanks to their sloppy lip-locks, she "wasn't a fan" of the "Entourage" alum at the time.
Watch Messing's "Watch What Happens: Live" appearance here: