Damn, sandman...I was all ready to go...
When I was in my mid to late teens and lived with my mom and brothers, I slept in the nude a lot, with my door locked of course (and I'd changed the lock to a real one with a key, not those chintzy bedroom door locks). I think it started after I read a book where a guy slept in the nude, and I thought I'd see what it felt like and turned out it was fun. Up to then I'd always worn briefs, shorts, and a tshirt. (Yes, I sometimes was overdressed for bed, but between showering and sleeping, I couldn't stand not to have that much clothing on, since I hated boxers.) I think about half the time I fell asleep with clothes on though because I was simply too tired to change after I'd showered after work or school and put clothes on and then spent time online until 2AM.
Then when I lived alone for half a year, I slept nude almost all the time, simply because it was easier than getting dressed, and I walked around the apartment nude much of the time too. (I was a teenage male without many friends and never dated; you figure out why the time it takes to get dressed or get undressed could have added up to a considerable amount of my day used up. ) At the most I'd wear underwear or loose shorts if it happened to be a cool night in the apartment.
Then, when I moved to Massachusetts to live with my girlfriend in her parents' house, I didn't sleep in a room with a door so I had to wear clothes. But my gf got me out of the habit of wearing briefs to bed (partly by telling me she'd always learned that wearing briefs constantly was bad for you, partly for...accessibility reasons... ). So I started wearing just shorts and tshirts and eventually started wearing real boxers (I'd never even owned a pair until then). Of course in winter I'd be bundled up in sweatpants and sweatshirt and another layer or two, since her parents refused to allow the heat to go above 65 during the day and shut it off completely at night.
Now I live with roommates, and I don't like having the door locked when I sleep because I worry (as I always do) about something happening and me being needed, or something happening to me and them not being able to get to me (like having a night terror, or something starting a fire in my room). Or simply them coming to wake me up early for something we'd planned and walking in during that particularly interesting stage of male sleep... So usually I sleep in boxers or shorts and a tshirt, lose the shirt during summer and sometimes the boxers.
If I lived alone again, I'd probably be nude much of the time, even when I'm not sleeping.