Most normal body odor doesn't smell bad to me. OTOH, certain types of sweat do. There's a point at which it turns acrid and rancid on people. I find that, oddly enough, I don't seem to have problems smelling most people who've been doing heavy work (indoor / outdoor), but that people who've been doing gym workouts tend to smell bad - that acrid/rancid smell to me. I've no idea what it might be due to. It's not the thought of what they've been doing. There's a distinct difference, usually, in the smell.

I can also frequently tell when people are ill from their body odor, and often what sort of illness it is. Strange.