think of you as sexist LOL but to the best of my knowledge, singular "guy" shouldn't be used in a unisex way. The only way guy is somewhat acceptable in a gender-neutral way is when referring to a mixed group with at least one guy (very French in that sense). Which I try not to use anyway, because these days you can say "hey people!" or "this is my person." Put it this way: I would never call you my nutrition "guy." Or my science guy.