A Bird of War from Always Sunny, the costume they dress up in for the wrestling match in The Gang Wrestles for the Troops, would be good if you're in shape...a funny tv show reference that some people (but not everyone) will get that allows you to run around shirtless.
I'm considering wearing scrubs and maybe a pot leaf hat and going out as a medical marijuana doctor. Or something like that. I'll draw a pot leaf on a circle cut from paper and tape it to the front or something. I'm not sure what props I'll have.
I love the douche bag idea, but I've seen that so many times before, plus I'm not enough of a tool to effectively pull it off.