From Lemminary’s link

An increasingly popular phenomenon at the time of the incident, coal rolling happens when a driver of a diesel truck floods the engine with more fuel than it can efficiently process, emitting a thick black plume of exhaust across the road. The emissions systems of diesel trucks are strictly regulated under federal law. But some truck owners modify their exhaust systems with illegal aftermarket parts, or fail to fix broken exhaust systems. In the 2010s, rolling coal became a kind of defiant act, an aggressive backlash against the increasing regulation of fossil fuels. People using forms of transportation that don’t burn oil—namely, those riding bikes, walking, or driving an electric vehicle—became targets. Social media apps such as TikTok helped drive the #rollingcoal trend. Videos with captions like “POV: You roll coal on every bicycle you see,” showing the engorged tailpipe of a diesel truck expelling a bubbling smoke, accrued thousands, even millions of views.