1) Plan ahead; I always start my costumes at least a month or two before Halloween
2) If you're making your own, make sure not to get too ambitious
3) Never show any bra straps, never wear something see-through, no sky high slits, and please people, no tube tops unless you are being a disco dancer, in which case, it better be a pretty modest tube top
4) BE CREATIVE!!!! Obviously if you go for a basic costume no one is going to be revolted, but this is a holiday for having fun so try to think of something original
5) If your mom would die if she saw what you were wearing, don't wear it
And now, the five worst costumes that I found while browsing Google (at least, the ones that didn't feature content so offensive I wouldn't dare to post it on this page):
Believe it or not, there were tons more where that came from. I'm talking completely inappropriate racial costumes, bestiality and, yes, prison rape. Please people, keep it PG!