I think I am. I think I'm nicer than most people (cringing at myself for saying that but I can't think of a humbler way to phrase it while still being honest).
It's weird that most people probably think they are nice, because that's pretty subjective. Like someone can be in the KKK but thinks he's like a really nice dude.
I think i'm nice because i would sacrifice a weekend to help a friend move for example, or do stuff for my almost elderly neighbour and so on. But no one could bring me to go to my uncle's birthday party and socialise with his friends, and i guess that's not very nice of me. So i don't know.
Yea, it's obviously not clearly defined. "Nice" is a box that we like to put people in or out of, but of course people and reality in general don't fit in neat boxes.
Being nice is more about what you do in a specific situation I guess. You can be nice in one situation, mean in another. Whether you are nice in general... Well how do you decide?