My wife's new thing is to go to random places like grocery store wearing short skirts and bending over to give guys upskirts while they shop. Turns me on when other guys get to see up her skirt!
I've always been turned on by men's reactions and ogling as much as watching a wife do this or similar.
To know that they are looking at her lustfully, imagining how good a fuck she is, or getting to put their hands all over her titties makes me hard.