Pete Wentz is a hottie, but he's also a total player. After hooking up with Rumer Willis last weekend, he's moved on already -- or rather moved back to Michelle Trachtenberg, Perez Hilton reports. "Pete confronted Michelle and they got into a heated conversation. Rumer kept trying to talk to Pete, but he was ignoring her," the spy says of the lover's quarrel. "Pete kept trying to touch Michelle's face. He soooo wanted to kiss her! Poor Rumer looked heartbroken."

Later on, when a group of girls asked Pete to dance, "Pete turns around, grabs Michelle and says to the girls, 'My girlfriend gets really jealous when I dance with other girls, right baby,'" the source says. Pete and Michelle ended up leaving the club together, and Rumer went home solo.

All of this comes the week of Fall Out Boy's Rolling Stone cover story, in which Pete disses former flame, Ashlee Simpson and totally denies their coupledom. "Maybe in a different universe, we'd be some hot couple, but not in this one," he told the mag. "I'm attracted to creative people and train wrecks, and there's no shortage of that in Los Angeles."

In our opinion, Pete is total He Did What? material -- and not in a good way.