I like your humor Nathan!It is exhuast soot, it builds up from the slow drive in traffic.
I get it on the front end when following a LMB M5 down the highway:hihi:
That crap is all over my bumper,i clayed the hell out of it,and barely removed it.Another source may be from the battery. The battery is vented below the car using a tube. If you have etching on the back bumper which looks like little black dots that don't wash off, it's likely vapor which is vented from the battery, swirls around the back of the car and gets on the bumper.
I think it's road tar that you can also find on the wheels. Generally, you find it most on the top of the rear bumper. I find that claying the car is the only diy solution to remove it.When I go to wash my car after a week or driving I see little black particles/dust all over the rear of the car. Looks like it might actually be stuff from the exhaust. Anyone else get this?