The cat costume, of course!

You pick the cat costume. Doffing your blouse, you reach for the tight sheeny black top. You put the top on first, shimmying your way through it, until your head pops out the neck. Then you reach for the cat ear headband, and place it on your head, being sure to straighten your hair so it goes on properly. It is then that you eye Mrs. Henderson taking a pair of scissors to the pants. She has read your email. She knows the rules. This costume may not obstruct access to your pussy. She shakes her head side to side as she snips, and then she hands the results over to you.

"Here. Put these on." She glares at you. "Slut."

You put it on. You slide it up your legs, and feel the distinct absence of cloth over your crotch. Your still-oozing pussy is bare for all the world to see. You shake your ass to make sure everything is as up and tight as your new duties need it to be.