[duo797]

I'm going to go out on a limb and guess that きめ comes from 気持ち悪い>> きもい＞＞きめー。　I think the jump from きもい to きめ is the same as 怖い to こえー or 面白い　to おもしれー. Correct me if I'm wrong, but that makes the most sense considering someone's being called 'gross'.