could you do a play on your name, or on where you live, or on how you know your friend? The best "funny" fancy dress costumes are when you subvert the theme - so I guess without a theme, something about yourself?
Ah thats the thing isnt it? Do you go as something where you still can look good or completely make a fool of yourself as with the matchstick idea. I must say I am leaning more towards the 'still look good' the more I think about it seen as I dont get out much these days!
I usually go for St Trinians girl/naughty schoolgirl, it's easy, you can usually buy suitable outfit form charity shops if you don't already have a white shirt, stripey tie, short school type shirt and a pair of Mary Janes. Hair in pigtails which you can back comb for that really naughty look. Plus take a satchel or music bag instead of a handbag.