I too believe the internet has opened up a whole new world for trolls to inhabit and multiply. I have a pathalogical hatred towards trolls (bullies) in real life and it has crossed over to online socializing. But more often then not I over-react in attempts to confront them & it is me that gets in trouble and goes down in flames.
I think I see a little of your confusion, if the person is being overly confident to the point of arrogance. Is it just confidence or is it arrogance ? etc. I have met both types in real life. For some reason, I who was more introverted would end up having as my closest friend a very confident/outgoing one. One was a real player/ladies man and another was just a very solid and loyal type.
My own feelings on how to differentiate involved how they treated me. Bulls (Alpha males) can tread on you mindlessly without malice. But the key is after you explain what it was that hurt you, they do not do it anymore. Things about myself of course might drive them crazy & so it was mutual, the need to modify... because you respected the others feelings.
So that would be I think the test of a healthy relationship. Do they care enough to value and protect your feelings. If they take the line, that that is just the way they are and you have to take it or leave it... then I would leave it.