Funniest costume we ever did was a sleazy pregnant bride and a sleazy bridegroom. I bought a tacky white lace mini-dress for $10 at a cheap-clothes shop, wore white fishnet stockings and white high heels, stuffed a pillow under the skirt and wore a ton of makeup and hairspray. My husband wore his own tux with the shirt open several buttons down to show his hairy chest, stuffed a sock in his pants to have a huge "bulge," wore a bunch of my gold chains around his neck, slicked his hair back and put a Cigarillo in his mouth. Cost us about $15 total. The best part was we had a whole sleazy wedding party with two pregnant bridesmaids. We won a best costume prize for this!
Another funny thing I saw was people dressed up to look like the host of the party. That always gets a good laugh!