Manners aside, when I'm around people I know (that is to say, there's no point in me pretending to be polite), for messy or impale-able food I stab it with a fork, and for grab-able food I use my fingers. There can't be much difference between eating pizza with your hands, instead of a knife & fork, and eating a sandwich with your hands, so hygiene hardly comes into it. I wash my hands unnaturally often, out of habit, and yet I don't suffer noticeably less from illness than people who never seem to wash their hands. This would seem to suggest that chopsticks have almost no use at all, other than for showing off and to keep your fingers clean.