In Ducky's case, I'd say mild OCD. McGee (or, as DiNozzo calls him, "the McGeek") is almost a textbook case of AS.
Abby's not so clear, but among her signs are marked eccentricity without caring what anyone else thinks, being more fond of her various computers and analysis machines than of people (to the point of naming them, and whispering to the DNA microassay machine that it's her favorite - whispering so the other machines won't get jealous), and of course her tendency to go haring off after a new conversational gambit because she thinks she's already explained everything to her coworkers clearly enough. I'd say AS, but stand ready to have this hypothesis disproved.
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Sodium is a metal that reacts explosively when exposed to water. Chlorine is a gas that'll kill you dead in moments. Together they make my fries taste good.