There's no excuse for a kid to not wear a Halloween costume. I've heard people say they're too expensive, but it doesn't have to be store-bought. It used to be that all costumes were homemade.
You can go as a cliché bedsheet ghost, wear your parents' clothes, even a put a paper bag over your head and call yourself The Phantom of the Opera... I don't care.
If one of your parents has a makeup kit, just use that.
One year I cut a bunch of holes in an old bedsheet and went as Charlie Brown after "having trouble with the scissors". Nobody got the joke, but I got candy anyway.
Besides, some costumes only cost a couple of bucks. The Dollar Tree around the corner from my house has cheap plastic masks and accessories that are under five dollars.
People are making excuses for laziness and lack of imagination. And on top of that, WHY would you ever WANT to go without a costume?? It's half the fun of trick-or-treating! If you show up without a costume and ask for candy- especially if you're a teenager- what that says to me is that you're only in it for the candy, and not the spooky stuff, and that you're just being greedy.
This isn't some anti-poor thing either. I'M poor. And yet if I really wanted a new costume, I wouldn't lie around and bemoan my inability to get one- I would look through my closet for old clothes, consider using something made of cardboard, anything at all, because I would feel embarrassed, even ashamed, to go out there and not wear one.
If my parents for some reason refused to get me one, I would fight for it. I would whine and complain. I'd rather stay home than not wear a costume. I would do anything to wear a costume.
So maybe if you don't care to have the complete Halloween experience, maybe you don't want it badly enough.