'rolling coal'

I did not know this was deliberate?
I always thought it was a malfunction of the vehicle!

https://en.m.wikipedia.org/wiki/Rolling_coal

Rolling coal (also spelled rollin' coal) is the practice of modifying a diesel engine to deliberately emit large amounts of black or grey diesel exhaust, containing soot and incompletely combusted diesel. Rolling coal is used as a form of anti-environmentalism protest.[1] In some jurisdictions the practice is illegal, due to it violating clean air laws.

I have never heard of it, but it doesn’t surprise me.

Ew.

Maybe it is accidental, but I saw this only yesterday. For a substantial stretch of road I had to keep my sleeve over my face.

Yesterday was the first I had heard the term....and that it can be deliberate and targeted...so not a malfunction of the vehicle as I always thought (and I'm sure sometimes is) but rather, possibly, a 'malfunction of attitude' ?