I was once at one of their concerts in '06.
A couple people(maybe 20 or so) were in the back waiting to see if they can spot people walking in/out so they can get an autograph.
Well everyone saw someone popping out of one of the busses maybe 20 feet away, so we all go out there except 2 girls, when we get back the girls had an autograph from wentz.
Not what I'd call a celebrity, but Pete Wentz broke my friend's phone a couple years ago. My friend was texting someone, didn't even notice yon douchebag, and he comes storming up to her, grabs the phone and smashes it to the ground, snarls something about how it'll be her face next.
My friend was a fangirl, so she was pretty upset about it, too.
I was working in the art department on a music video at Pete's bar in LA a few weeks ago for his crappy new band. He decided it would be a great idea to get wasted on set.
Near the end of the 18 hour day, I started cleaning up. I was minding my own business and scooping gumballs and broken glass from the stagnant bar sink water. Yes, gumballs. Bubblegum was the theme of the video and he poured a 3 pound bag of gumballs on the singer when I had instructed him to throw one handful at her and one at the audience.
Pete stumbled over, looked at me, looked at the sink, looked at my gloved hands, and said "This beer isn't f*ckin cold enough." He proceeded to pour an entire pint of corona on my hands and arms (I was in such shock I didn't think to move them immediately).
I looked a him incredulously.
He shrugged and walked away.
Pete Wentz poured beer on me. On purpose. He's an asshole.