Abandon painting.

You lean the painting against a wall and set off walking. You've only gone a matter of yards, however, when a tall, heavily-built stranger jumps out in front of you. Naturally, you give way.

He gestures a large, bloodied knife at you. "Hand it over," he says.

You can:

Look behind you in case his accomplice isn't there weilding an equally big knife.

Try to fight your way past him.

Say, "Sure, it's three blocks that way", pointing in a random direction. Hey, it's worked once...

Say, "I left it propped up against that wall back there".