[sdwr]

It's the sweat production. Imagine someone sticking their hand in their armpit, then shaking your hand.

Vs putting a hand on their bare hip, then shaking your hand.

Also, groin sweat smells different and probably has extra hormones/pheromones in it

[ssl-3]

I imagine that every time I shake hands with someone.

Maybe that didn't just remove their KFC-greased, butthole-stinky finger from their nose before we shook hands, or maybe they did.