If dressing up is the best part of Halloween, coming up with a good costume is the worst. Even though it falls on October 31 every year and even if you spend weeks thinking about it, we've all been guilty at one point or another of waking up on October 29 with nary an idea of what we've going to be. In the end you find yourself stopping in at one of the multitude of costume stores and grabbing something off the rack and spend all night wondering how you ended up in a situation where you were a banana for Halloween.
It only gets more complicated if you're in need of a couples costume. Not only do you have to think of a costume idea, but the other party has to sign off on it. Do you really want to spend the lead-up to Halloween negotiating the terms of a costume? Of course not.