As an adult, I push my testicles back up into the inguinal canals (where the testes are stored before they drop when you're young) for pleasure. It doesn't hurt in the slightest, and they don't go up there naturally unless I'm wearing something really tight, like a wetsuit or climbing harness.
I'm curious to see if anyone else does this and if it's a thing, or if it's just me.
Not a thing I have heard of or done.
I haven't been able to do it since I was maybe around 12 years old, and it would be very painful indeed now. I read once that sumo wrestlers train themselves to be able to retract their testicles, but after a quick search, it sounds like that may not actually be true.
As long as yours aren't internal for extended periods of time though, I'd be surprised if it could cause any problems.
I’d like to think I try most things. But not this. My testicles are just too sensitive where they currently live. I don’t think I would enjoy it.
10 Weeks Healed Post-Circumcision - Salt Washes, Random Stitch End, Post-Nut Soreness/Swelling. 
Do you pull your foreskin back when peeing?
How far back should foreskin retract when erect down the shaft?
one week in from circumcision 
14 days after circumcision.
