Don't stop. Don't talk to them. Give them nothing. Stay on the main road/footpath. Alleys seldom have witnesses. The more you ignore pricks on the road, the worse it gets for them to try and justify their aggression in a court of law. This individual driving the van deserves to lose their license in my opinion. A total and utter disregard for other road users.
Get over it mate, it's just a tacky bumper sticker meant for laughs, nothing to be taken seriously.