I like to think that when invited to a costume party you can be one of three kinds of people:
1) Lazy turd - Can be found uttering "I came as myself" all night. Never be this person.
2) Half arse - Can be found uttering "Yeah I left it to the last minute" all night. You can be this person if you aren't really close to the person throwing the party. You were nice enough to wear a costume. You pass, but only just.
3) Full costume - You won't be uttering anything because you've adhered to the requirements of the party, well done. If you're experiencing ongoing costume related discomfort, you're doing it right. Clearly dressing up in a full costume is the only option!
Now that I've convinced you to dress in a full costume, here's some basic costume party protocol:
a) Stick to the theme: it's basic, but the most important. Don't be the wanker who shows up as The Joker at the Bollywood themed party.
b) Keep it simple: make sure people can quickly identify who you're dressing up as. If you have to explain your costume, you're not getting your message through. People will recognise Darth Vader, but they won't recall the fat guy in the Rebel Squadron so easily.
Cliche Super Mario costume. Uninspiring, but widely known. Don't mind the hand gesture.
c) Do it yourself: where possible, try and do the costume yourself. Don't just go on ebay and look up a costume. It's so sterile and generic. Be creative. You don't need to sew anything. You could just make a little accessory (see hat in the above picture) or use something existing in your wardrobe in a creative way. A red plaid shirt and red suspenders used in a lumberjack costume:
Belt and shoes don't match - fashion crime.
You have to remember it's just a costume party - it doesn't really matter how polished your costume looks. If anything, you're expected to look stupid. Above all, make sure you have fun with it and never cover your body in paint - it goes everywhere:
"I blue myself."*
*A homage to Tobias Funke from Arrested Development.