Man rash is the condition that results from wearing certain types of boxers (especially flannel) on a hot day. The sweat soaked boxers will begin to cause a form of chafing very similar to diaper rash. This condition is more common in big men, as they tend to sweat more and their thighs rub together more. A man suffering from this condition can often be seen walking in a bow-legged manner.
Man Rash is also believed to be the biggest driving force in sales of baby powder to men.
Hiker A: Why the hell are you walking like that? And what's with the cringing?
Hiker B: I've got a wicked case of man rash. It's killing me.
Hiker A: That's what you get for wearing flannel boxers to go hiking in 99 degree weather? Dumb-ass!