People who behave stupidly, riding the edge of decency with reckless disregard and having absolutely no discernable reason to be doing so.
There's a certain amount of awareness that I look for, and these kinds of people display none of that and push everyone's buttons for no apparent reason because they can. Screw that. It's immature and very very rude as well as being a sure way to make enemies.
Some people mistake it for realism, I assure you it is not, it is handwaving behavior away that we should probably reflect on and possibly discourage.
Fortunately these kinds of people who truly do this are rare, and they slip and fall into the darkness soon enough. But they are very irritating, and riding the edge even if you're not reckless and unaware is very much the same sort of irritating as well.
Sometimes it is easy to get overconfident. That's no crime, but it can reduce one's awareness of many things.