I was a Scoutmaster in the Boy Scouts of America for about ten years. I'm a pretty big fellow and sometimes a little rough (although in the nicest way), so some of the scouts referred to me as "Rexbo", based on the Sylvester Stallone movie and the Gary Larsen cartoon that made fun of it.
Psycho Killer
Also based on my Scoutmaster career, this was based on a game I accidentally invented where I played a psycho killer catching scouts. For some reason, even though I was overweight and considerably older than the scouts, they insisted on me starting the game as the "psycho killer". One of them remarked, "You're pretty fast for a fat man."
The Giant Mutant Prairie Dog From Hell or "Prairydog" for short
While working with one fairly colorful character in the cubicle next to mine, I heard someone say my name. I stood up in my cubicle and my coworker began to laugh. Seeing me pop up like that, with my brown hair and full beard and natural cuteness, not to mention my large 300-pound frame, he said that it looked like a giant mutant prairie dog from hell coming up out of the ground.
Pluck 'n' Chuck
I suffer from occasional hypoglycemia, which manifests in extreme agitation. I've never really hurt anyone, but coworkers used to tell new people on the floor to always make sure I was adequately fed, otherwise I would find someone, pluck his arms off his body and chuck him [the person] out the window in pursuit of them [his arms]. This behavior was also described as, "Pluck 'n' Chuck." I've never actually done it, at least that's the "official" story.