I suppose it can potentially leave the realm of "harmless" if they're driving a vehicle, but people with no spatial awareness. Not looking where they're walking so you have to dodge them, obliviously blocking a walking lane, taking one step out of a doorway and immediately stopping to check their phones, etc. Shit drives me up a wall.

The closest I ever came to a fistfight was when a couple of guys in front of me going down an escalator side-by-side after a hockey game took one step off and just stopped. Obviously I had to shove them out of the way so we wouldn't be crushed by the slowly-descending wall of humanity behind us, and they took offense to that.