Halloween Theme Costume T-Shirts. Thinking about your next Halloween costume party, but not really wanting to get all decked out from head to toe? Looking for something easier and simple to wear for that last minute party or holiday get together? Well, the T-Shirt Costume is for you! With t-shirt costumes you can dress them up or down according to the look you want. Add an accessory of a mask, wig or hat to give your costume the edge it needs to stand out above all the rest. Everyone has a favorite t-shirt thatís worn in and comfortable to wear.