With my own rig it would have to be looking clapped out and falling apart. For others it would be those who find it funny to drive off trail, and even worse is those who stand around and think its cool and cheer them on.
The sound of junk jumping around and joints not being greased also bugs me.
lack of maintenance in general really bothers me. i see alot of people that do next to nothing to maintain there junk. aslong as it continues to run there not worried about it.