I don’t either. Matter of fact, I did this exact same stunt yesterday in my SUV to a punk trying to cross into my lane from 3 lanes over.
He backed off and we traded birds. Big deal....another day on the highway.
People are getting weirder all the time, you never know. I just ease off and let them go. Not in the mood for a running feud down the interstate, personally. Just going from point A to point B and would rather be left alone as much as possible, so jerks get a pass from me. If their day comes and it probably will, I won’t be the cause of it.
When proffered the universal peace symbol from a passing motorist, I put a big ear-to-ear smile on my face and enthusiastically wave at them. You should see the looks on there faces as they pass by, it's hilarious.