As a child, I was a tube of Crest toothpaste (with a cap for a hat). Now that I'm an adult, I tend to go for sexy or historical costumes (Victorian getups, dominatrixes, punk girls, medieval princesses, etc.)...
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If you're not opposed to spending some money and renting or buying one ready-made, there are a lot of options. But it's also fun to be creative and put a costume together yourself...

I usually go for something sexy or semi-sexy too, unless there's kids attending then I go for funny.....
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But for adult parties, some of the one's I've made are:..
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Cleopatra (my hair was dyed jet black then, wore a tight toga across one shoulder with lots of gold as the trimmings, the choal make up....
A flapper (got a slip and sewed on strips of that shiney stingie stuff with the right shoes and a kinda sequenced band thing around my head)..
Hawaian girl (spent about a week making that grass skirt damn I wish I would have kept it)..
Prostitute (no need for explanation on that get up ... anything goes lol)..
SheDevill (bodysuit with a stiff tail, a collared sheer cape, and pitchfork ..
Vampiress..
50's bowler girl (one of those wide skirts with a poodle at the side bottom and crinlin under it, a top with a big A on the left, bobbie socks, hair and make-up to match) ..
60's girl and 70's girl (both funky dress, right shoes, glasses and the appropriate do and make-up)..

I'm more into joke costumes. A cereal killer, a used tampon. Etc. For the majority of middle school, though, I went as a vampire. Just because I liked wearing a cape. Hah...