How would you describe someone's attitude?

Firstly you see if the person is worth you attention then you see how he or she behaves, does she have two different personalities? Is he or she shy, proud, crazy, dumb or just plain? How does he or she treat you? Does he or she complain about someone or you behind you back (because if he or she does then you should just stay away if you do not want to get into any kind of trouble) etc. Based on these few things you can describe her attitude but if you want to say it on his or her face then:

1) If it is something good - go ahead tell him or her how awesome he or she is.

2) If it is something bad- say what you feel like in a gentle and polite manner if you do not want to get in a fight.