I'd grab one of the store microphone/PA handsets and announce that this store is a GUN FREE ZONE and no firearms are permitted in the store. He'd leave. Problem solved.
Yup,, or go home grab my double barrel 12 gauge, and shoot it into the air, if that didn't work then I would purchase a pair of scissors and attack him with them! Then I would throw up on myself just in case he wanted to rape me!