I came across one of those guys who MacGyvers their vehicles to emit extra exhaust

[Xithras]

46. As an FYI, most poorly maintained diesel engines smoke under hard acceleration.

Diesels run a much richer mixtures than petrol cars, and are far more susceptible to smoking under acceleration. There are a number of things that cause it (partially burned soot buildup in the exhaust being vaporized during hard acceleration is a common one, and dirty injectors are another frequent cause), but most can be traced back to poor maintenance. No Macguyvering required. My dad has an old Dodge trail truck that he uses in the backwoods in Oregon. Under load, the thing belches black smoke like it's burning coal or something. It's not modified to do that...it's just an old fashioned piece of crap.

The guys who modify their trucks to smoke generally do it when they're cruising or idling. The fact that he was only doing it as he accelerated suggests that he just had a shitty truck, and was being an ass about it.