Simply rate the user's above "niceness" and cooperativity from 1-10. Tell them how they could improve, and be constructive. And tell them why they're nice :)
DO: 6/10. I think that you could be a little less critical, and maybe more open to new ideas.
DON'T: 5/10 You're bad.
If you don't know the user above, simply come back later when another person has posted.
JUST PLAY THE FRICKIN GAME
Don't do like 100000000/10 or anything. 11/10 at MAX.
PLEASE SAY WHY YOU LIKE THEM GOSH DARN IT PEOPLE
:)