The surefire way to determine noobness - frequency of the use of the word 'noob'.  The more a player calls others noob, the bigger noob they are.  That, and anyone who uses 'pwn' to mean own.  Skill players don't bother stating the obvious.  They just kill the noob.

Team damage on.  Sure you get a lot of moronic tkers who think it is fun or funny, but that is more a problem of not having admins online to permanently ip ban them...