1. Shave your head. Preferably at a salon in front of a large window. If that doesn't scare them off, then
2. Choose a weapon. Baseball bats are good, but don't convey the stratospheric level of crazy that you want to get across. Instead, opt for a large green umbrella, brandished with abandon. A baseball bat says "I came prepared to beat someone/something," while a large green umbrella says "I just snapped, and this is all I could find in my car to be an extension of my unmitigated rage." Next,
3. Choose your outfit. White gym shorts, tennis shoes, and a hooded sweatshirt are recommended–not only for freedom of motion, but because when coupled with your shaved head, wearing these items will make you appear, at least from a distance, like Andre Agassi. And the paparazzi don't mess with Agassi. He's like paparazzi kryptonite.
4. Then, wait until all of their lenses are trained on you, and attack the nearest SUV with a green umbrella. The paparazzi will instantly turn away, bored. In fact, most of them will probably fall asleep behind the lens, possibly even letting their cameras slip from their sleepy hands to smash on the concrete. (If so: bonus!) I mean, how many times have paparazzi seen former pop stars dressed like Andre Agassi beat a car with a green umbrella? Like 900 or something? It's been done.