Anyone seen any pickups with modified pipes that come up through the pickup beds, and resemble the pipes used on big diesel trucks? I think they are called
"Bullhorns". (Sorry, I'm not up on this stuff) Someone in my area has such a truck, and apparently, the operator can cause thick, oily smoke to belch from those pipes
at will. So, why would anyone want to do this? I can only think of Occam's Razor: The most simple explanation is usually the right one. They have this done to
cheese off others, say cyclists, or anyone who is driving an environmentally conscious vehicle such as a Nissan Leaf or Toyota Prius.
No idea who the one is in my area, but I've seen him enough times to conclude that he does take some kind of pleasure in using his vehicle, and smoke equipment,
to harass and intimidate people. As the OP stated, some do like to intentionally mess with cyclists.
Doesn't pop psychology have a word for grown men with the minds of fifteen year olds?