A term used when one is getting ready for a "slutty" party (i.e. Halloween parties, lingerie, etc.). Resembling "suit-up", to "slut-up" is preparing for action. Ideally it is the "outfit" with the least amount of clothing.
Slut-up! We are going to a Halloween party!
by CKJONPLASCENCIA November 02, 2012
imp: a derivation of Barney Stimpson's "Suit up!" (CBS's How I Met Your Mother); an imperative to put on one's sluttiest finery
"Barney told Robin to "Slut Up!"
by Adolf Oliver Bouchere May 27, 2008