I was gonna title this "Dirty Butt", but came to my senses...

The rear end of my car has a lot of small black globs on it - from pops and bangs, I guess. It didn't all come off when I washed it - what would you recommend to clean my (car's) butt up?

 

I have that too... I figured I'd use some detailing spray on it or carefully pick them off. I'm surprised it didn't come off with a washing. "Dirty butt" would get you 2x the replies.

 

I think I notice the same... When I took delivery (my car was used), I clayed, polished and sealed the paint. Between the clay and the polish, all of this gunk came off and I think the sealant is helping further buildup to just wash off with car soap.

You can typically get a clay bar kit from your nearby auto parts store that contains a spray bottle of quick detailer, used as the clay lubricant. You shouldn't need to use your fingernails or anything abrasive.