By professionals:
Genius, bookworm, antisocial [someone needs to get their definitions straight], asocial [better], short-tempered, bipolar, OCD, quiet, loud, nice, sweet, smart, know-it-all, mean, selfish.
By strangers and people I barely know:
Eccentric, weird, nice, polite, awkward, quiet, helpful.
By friends:
Eccentric, weird, smart, Wicktionary, Wickedpedia, freaky "in a good way," bipolar-in-the-brain-department [because I never know 7 + 8 without taking a moment to think about it, but I tutor them in almost everything when they ask for it].
By non-friends:
ret*d, b***h, stupid, awkward, clumsy, loudmouth, dumbass, smartass [why thank you], lazy, special-ed dropout.
By me:
Lenny, Wicked, eccentric, Wicktionary, asocial.