I've seen several towbars left on the nose gear, hit with the propeller. A chunk of one just missed my head. I've seen them jam the gear doors on a few aircraft, too. Someone brought me a Bonanza a few years ago, and when I pointed to damage to the nose gear doors, they said "bet you can't guess how that happened." I told them it looked like they left the tow bar on and went flying. They did.
It's a lot harder to leave a power tow on there, and taxi, but not impossible.