Many things are strictly American; bumper stickers may be right at the top. They are an interesting phenomena: pithy statements that give insight into the values, interests and loyalties of the car owner. The subject matter varies widely, and the number a single vehicle sports gives a clue to the vehemence of the driver's opinions and passions. They range emotionally from humorous to in-your-face aggressive insistence. Sometimes the combination of numerous ones on a single bumper reveals the thoughtfulness (or lack of it) in the person's views. Some never fail to irritate me for their sheer superficiality--like COEXIST, written in all different religious symbols, or VISUALIZE WORLD PEACE. Of course, a very clever person followed that one up with VISUALIZE WHIRLED PEAS--what a hoot.
The one thing about bumper stickers that I find most curious, it that they happen to be on car bumpers. You may ask, "Well, where else would they be?", but that is not what I'm getting at. There is a quasi-anonymity to posting something on your car. You get to have your say, and no one can talk back. Other drivers only get a brief moment to read them, and then the opinion-expresser has turned the corner, never to be encountered again. Yet, there you are, with that person's opinion splattered on your brain, as messily as a bird dropping on your windshield. You can't retaliate if you disagree, so it just sits there and annoys you till you wipe it off.
Rude and profane ones only reflect back on the person posting them. Somehow it doesn't make me want to introduce myself. One is always wary with a person who intentionally and belligerently lays it out there. It is my observation that in the political realm of bumper stickers, the Democratic/liberal/rude/profane ones seem to out number the Republican/conservative/rude/profane ones by a ratio of at least ten to one. (I'm really being generous to the Dems by using that ratio, because off the top of my head, I can't recall any rude/profane conservative bumper stickers.) It makes sense--a liberal isn't as tied to traditional polite manners. A conservative by nature is more reserved. Each time I encounter a disrespectful, slanderous, or vulgar political bumper sticker, the feeling of getting pooped on returns, and that, my friend, is probably the exact intent of the individual who posted it.