What to wear: Fancy dress shops have plenty of different versions of cop costumes, so if you search for one in a khaki colour, like a state trooper, your Hopper costume will be complete. Grow out or stipple on some five o'clock shadow if possible, and maybe carry around an empty beer can for good measure.
How to act: Picture your most hungover, irritable moment, and then try to keep that attitude going all night.