Do the Monster Slapdash
Load a bunch of videos of babies into this thing and then go around the party showing them to everyone. Your costume is New Parent, but you'll only get to explain it to a few people before the other party goers start actively avoiding you.
Kludge (klooj, n.): a clumsy, inelegant, improvised solution to an engineering problem. Kludge-O-Ween (klooj-oh-ween, n.): a makeshift, half-assed solution to Halloween. When it's too late to worry about finding the perfect costume, it's time to realize that ANYTHING can be a costume.