What to Wear: I'm so sorry, but you're going to have to start with a Make America Great Again hat. Then add a plaid shirt, an apron, a "Gary" name tag, and find some way to make your left arm look like a stump. Tada!
How to Act: Gary's a little insidious, honestly. He seems nice, but you can tell there's evil brewing inside him. Try to manifest this fake-nice creepiness.