Jeremy Piven's guest-starring turn on "Will & Grace" as the ex-boyfriend of Debra Messing's character was unforgettable for Messing - but not for the reasons you might think.

"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.

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Her favorite male co-stars were Harry Connick, Jr., who played Grace's husband Leo, and Bobby Cannavale, who played a love interest of Will's (Eric McCormack), she told Cohen.

Watch Messing's "Watch What Happens: Live" appearance here: