Hmm, there's different kinds of "dangerous" other than just physical. The definition extending a bit, I might classify as that.
Normally I'm polite and caring, but sometimes I run into someone who is an absolute jerkwad or bully, constantly causing problems for me or friends of mine, and in THOSE cases, I can get... manipulative, vindictive, and unpleasant.
The best two examples.... number 1 was back in high school. There were plenty of bullies and just unpleasant individuals in that school, but one of them really stood out. He'd CONSTANTLY pestered me over the 4 years, pestered ALOT of people, tended to get right up in your face, and just, well... yeah, kept going from there. During senior year, getting somewhat near the end, he pushed me just a BIT too far. I knew full well that he was branded as a bit of a troublemaker, and knew also that it was likely that the faculty were probably not very happy with him in an overall sense, so I.... capitalized on this fact. I was on very good terms with MOST of the faculty, and most of them knew me (including the principal and those that worked in the main office), and, without actually breaking any rules myself, well... I'll not take a million years to explain the process, but after I was done, everything was stacked against the jerk, and he was either held back or expelled, as he'd hit the "last straw" situation due to what the faculty now knew about him.... I dont quite remember which of those it was (I knew at the time), but he didnt graduate that year. Ah, the horrid glare he gave me after these events. Wont forget that.
There was also the time I worked at the theater, and after a decently good day, my idiot manager at the time found that the till was short 20 dollars, and decided that I must have lost it somehow (it was easy to prove that I didnt STEAL it) and decided it was time to fire, immediately. I knew she wasnt the brightest bulb, and there was a high chance of her having simply made a mistake, but not only would she not acknowledge this, she also didnt heed the warning I gave her after this, as she was quite sure that a low-ranking employee couldnt REALLY do anything. Turned out to be wrong. It turned out that it wasnt too hard to contact one of the guys on the highest tier of the food-chain in that company, and... well, it didnt take long at all. 3 or 4 days, and she was out of there. ....and in the process it was found out that SHE had lost the money when moving/counting/something. SURPRISE. Normally, I was fine with being fired... I knew I was a terrible employee in many jobs, with my inability to communicate, and general constant desire to be anywhere else, but being fired for a reason that hadnt even happened didnt fly, really.
There's way more detail for both stories, but yeah... that sorta thing is what happens. Fortunately, it's very rare that it occurs... I tend to avoid meeting unpleasant sorts most of the time, and I am not in school, nor do I work anymore, so the two types of places most likely to cause that are gone for me now.