Embarrassed in sports
 

Instead of allowing your slave to wear normal underwear make them wear either no underwear underneath jeans for a day (which will cause chafing) or dont allow them to wear underwear under their sports kit, so if they fall over or crouch everything will be revealed (works best for a male slave). This could be embarassing, particularly in rugby where you wear loose shorts and spend a lot of time on the ground.
Good luck anyone who tries this.

Hmmm, not so much a dare more a punishment!

Form personal experience it doesn't cause much chafing, might i guess if you made sure they were shaved, can get itchy if they're not freshly shaved, say shaved a couple of days ago so a few hairs are just coming though

What? I'm a student, washing clothes is a hastle, it's so much easier to go commando. (that make me a skank?)

how about have them wear female underwear if it is a guy or granny panties if it is a girl?