These are all incidents I either witnessed, saw the aftermath of or had related to me:
Punching a passenger in retaliation for being punched by them is a way (A coworker at my current job got fired from an airline for that).
Driving your tug and bag carts underneath the jetway, and clipping the jetway steps and flipping the last cart over.
Running your tug inbetween a marshaller and the a/c and hitting the a/c's nose with your last bag cart, causing over $1 million in damage, and the airline retiring the a/c 2 months early.
Leaving a carryon cart inside of the containment area and have the prop on the #1 engine strike it.
Slacking off in your duties. Had a guy on my gate crew @ FL
that was fired because he wouldn't help the rest of the crew load planes after cleaning them. He'd just go sit in the pillbox until the next plane came in. And at this particular time, our crew were responsible for 3 gates, and needed every person at all times.
I myself was fired from both airlines I worked for, for reasons mentioned in earlier posts. The guy that got me fired from AirTran got a little karmic retribution a few months later when he suffered a collasped lung one day while loading a plane. The guy that got me fired from ASA kept saying "I didn't want to get you fired." When I was fired from ASA, I had already been on a short leash with the ramp manager due to some angry flareups I had out on the ramp (I used to have an anger problem), and this guy knew it, so he basically took my joking around with him the wrong way and got me fired right at Christmas time. Pretty much the entire gate crew chewed the guy out for his actions. I could have appealed both firings, but I was so angry at both companies after I got fired, that I decided I did not want to persue it.