Push him away and slap him

You did not sign up for this! You shove the guy away and slap him full across the face. Everyone in the general area turns around to see what just happens. He looks stunned, and stumbles away, "Fuck! That hurt, bitch!"

You don't back down, "You touch my ass again, I will fucking kill you."

He looks around embarrassed to see if anyone heard you, and notices that pretty much everyone within earshot is listening in.

He pulls himself together and looks at his friends, "Let's get out of here. She's kind of a dog anyway."

You're not sorry to see him gone, although it means you lost out on signing up his friends for the mailing list. You put the whole thing behind you and get back to giving demos. You collect 22 business cards over the next half hour. You can live with that.