The violent scammer
"I'd been working in the same downtown pub for five years (great little hole-in-the-wall... so fun, but super-dodgy sometimes) and had somehow managed to be the only server there who'd never been assaulted. Never shoved, bitten, spit on, hit, etc. Like I said, dodgy.
"We'd get a lot of good ol' boys (read: crotchety old assholes who think it's super-cool to be leering, gross misogynists older than my father) and one of them was a million years old, tiny, and frail. On this occasion, he wanted to pay for his pint with a credit card but didn't want to get up, so I ran it through and brought back the slip for a signature.
"Twenty minutes later, he called me over and told me that I'd stolen his Visa. Of course assuming he'd checked his wallet, I panicked for a second and checked my apron and the machine to see if it was there, but no luck. When I went back over to tell him I couldn't find it, his wallet was open on the table with the Visa peeking out. I pointed it out to him and he started yelling at me that it wasn't there.