duct tape a large bag of powdered sugar in a ziploc bag to the bottom of a payphone. watch for passers by and then call it. When someone answers tell them the package is taped under the phone. If they grab it, run up and slam them against a wall and act like undercover or a pissed off druglord. This might scare the shit out of them more than make them think your weird, but it should be fun.