I have never chafed "down there"....today I did a 12 mile run on the treadmill (90% of my running is on a treadmill). I have done 6-10 miles countless times with no issues and no body glide. I was sweating a lot....but that is nothing new. When I got in the shower after it felt like someone was stabbing me in the nads (sorry...crude). Why would this all of sudden happen? Ever just happen all of a sudden to you? Busted out the Desitin to help out....I have 30 more miles to run this week.
edit...I have been doing the bulk of my running in tri shorts.....was wearing running shorts with compression built in today. Same type of shorts I have worn for years training and completing marathons in.
So.. are we talking chafing on the actual "cash and prizes" or more in the "gooch" area?
I sometimes chafe on run distances that I haven't in the past, and not necessarily on my longest runs... sometimes stuff happens. It might have had something to do with the angle of your dangle in the compression shorts during the run. I would imagine the treadmill would just add to issues. Poor ventilation, and more repetitive than outdoor running.
Body glide is good for both preventing chafing and helping chafed areas heal up...