May be worn by both males and females.
Exact meaning of the use of "nut" is unclear but could refer to: 1) clothes that a man has nutted into or used to clean up nut spillage, 2) the looseness of the shorts revealing the man's nuts, or, 3) the ratty nature of the clothes, like the unkempt appearance of a wild, unshaven nut sac.
Dick: Nothing really. Probably going to spend Saturday and Sunday in my nut clothes, watching football.
Harry: I think I'm going to have to break down and get new nut clothes because the old ones are so nasty that even I can't take it anymore.