Mismatched couples.  I'm not saying you have to be co-dependent and color-coordinate on every other day of the year, but on Halloween, come on!  You've got a partner.  Dress like you know one another at least.  Given how many options there are for couples costumes, why would you go as a witch and he as a gorilla?  Makes no sense.  See a counselor.

When boyfriends won't dress up.  Yes, it's a possible corollary of the above, but it's even sadder.  Not coordinating your costumes is one thing.  When the girlfriend trades out her dignity to go as a slutty [insert random profession here] and the boyfriend can't do any better than the baseball cap and jeans he wears every other day, that's just sad.  Ladies, I'll graciously extend the offer to be your revenge fuck whether you're looking for an excuse for a breakup or a rebound from an already-realized one.

Overpriced haunted houses.  Needs no elaboration.

Punny costumes.  The joke lasts only as long as it takes to get it, and if you've done it right, that's not long.  On the other hand, if you are too obscure, no one will care.  In fact, I don't in either case.

Orange lights.  The official colors of Halloween are supposedly black and orange, but that's only true for things made out of construction paper.  Black lights are cool.  Green is creepy.  So's purple.  Strobes are fun.  But orange?  No.  They look like faded xmas lights, so could you just wait a couple more months before you pull those out of the attic?

Reruns.  You think you can get away with the same exact costume again, maybe the next year or maybe even a few years down the line.  Look, unless you've moved to another state, we're going to remember.

Spiderwebs.  They look good, but the stuff is just plain hard to work with.  If you don't take the time to do it right or just don't have a clue what you're doing, then don't.  Otherwise the result will look less like you decorated than that you were pranked.

Autumn does not equal Halloween.  Halloween is about spirits, not harvests.  I like jack o'lanterns, not pumpkins.  I like scares, not scarecrows.  Get with the program.

Masks.  On me, they're annoying.  It's hot, I'm breathing in my own breath, and I just can't see.  On other people, it annoys me because I can't see facial expression and (at parties and other get-togethers with friends) I probably won't recognize you until you walk up to me and tell me who you are.  I'm okay with makeup and appliance prosthetics, but full-face latex masks are just annoying.

What's your line?  How hard is it to say "Trick or treat"?  I realize that as traditions gain traction, sometimes their origins are lost, but when kids don't even ask "Trick or treat?" before expectantly opening their sacks for candy, we've lost something.

Unrealism.  The supernatural is one thing.  Monsters are imaginary.  Artists have free reign to run with their ideas.  But body parts?  Skeletons?  Those are grounded in reality.  I mean, seriously.  How fucking hard is it to pick up an anatomy book and turn out a decent-looking skull for fuck's sake?!

Halloween hypocrits.  If you put out decorations and don't give out candy on the most important night of the year, then you're a bully.  That's just what you are.  You tease children.  Just die already.