i'd have to agree so some extent with cossins on the sack-sweat and boxers bit - when it comes to some heavy excercise with your body and possibly even in some damp surroundsing - i'm thinking like going mountainclimbing in the summer or something like that - the sack does get sweaty, and with boxers the biggest problem isn't that the sack gets sweaty, but that the sweaty sack gets rubbed against the sack-owner's thighs, because it just dangles there and isn't fixed with the underwear, and thus can result a rash at a very unpleasant place  :? ...but as i said, that usually happens when it comes to mountain-climbing, because the legs are streched up further then when you walk normally (that's why the sack gets rubbed against them) 

p.s. god! if i left out a few words, this post would have a totaly different meaning!!