I used to have "Guns cause crime like flies cause garbage" on my truck, also one with Hitler and Clinton with right arm raised "All in favor of Gun Control raise your right hand". Plus a "Read Your Constitution!" from the JBS.
I recieved many positive comments about them, and several negative ones.
One in particular in a shopping center parking lot that I am quite proud of keeping my cool. A woman at her car calls over "Hitler and Clinton? whats wrong with you?" I ignored her and started loading the truck with bags. She again calls over "Well? just what is that supposed to mean?" I took a deep breath and calmly stated that "The Clinton Administrations track record on individual freedom and liberty is terrible, especially when it comes to the rights of law abiding gun owners". She says pretty nastily "your full of sh**". I replied that "I may be full of it, but I'm not the one verbally attacking a total stranger, cursing in front of children (my daughter about 5 at the time was with me) because you see a bumper sticker you don't like". She absolutely exploded! Jumped in her car slammed the door and squeeled wheels out of there! If looks could kill I'd be dead. An older couple walked by having heard everything, the wife leaned over to her hubby and said "what a nasty bi***". That comment alone made my day, I was starting to self critique and replay the situation in my head to see how well I handled things making sure my tone never got out of hand when she said it.
I remember this encounter vividly because I'm usually a hot-head and blow my top pretty easy. It took me great effort once the adrenaline started pumping to keep my cool and stay rational.
This is how you beat them, remain calm, be rational, state some facts and non-challantly prod them into becoming unglued and making themselves look like a nut!!