Trying on a character for size

Generally speaking, I'm a pretty nice person. A nice friend, teacher, daughter, wife...not to say I don't have my sparkling moments of snarkitude because we all do, but as a rule, I try to be nicer than not.

However, not all my characters are. Recently I was finishing a book whose protagonist was a queen bee type in her high school. She's the sort who is very competitive, even with her friends, and who expects that she will always get the prize. Always. And if she doesn't, she is NOT happ...