Then there are a lot of guys making a sincere effort to be nice that get frustrated with their life experiences and explode.

This is the only part I really disagree with. There shouldn't need to be a sincere effort to be nice. Being nice should just be you, otherwise it's not really being sincere. At least that's how I see it. Otherwise, I think I agree, even identify with it. I'm a very much shy and introverted person, and recently moved to a place where I don't know anybody. I'm trying online dating and matched with one person. The short story is that I think my new surroundings, my loneliness, and various other factors get to me and I let my insecurities and anxiety come through and said somethings that I think scared her off. I like to think I'm fairly self-aware, and genuinely think I'm a fairly reasonable and level-headed dude but I let some stressors get the best of me this time. Does that make me a "nice guy"? If you asked this other person I matched with they might say yes, but I'd say I had what was an otherwise uncharacteristic interaction.