let all the air out of your lungs, a compatriot bearhugs so you cant suck in air, you pass out. Take turns, it was a way to amuse ourselves at the age of 13-15. Tried it a couple of times later in the ring so you would know as a holder when to let your opponant go before damage sets in.
Dont think sex would be enhanced by it. To me that takes all my concentration, no distractions.
thanx,
bill