I'm pretty sure they're talking about popcorn tunes (also called "crackle tunes") which intentionally makes your car backfire so it sounds like a poor man's version of rally anti-lag, but in the process destroys the catalytic converters, fuel efficiency, power output, and is generally obnoxious. Rolling coal isn't even a thing in Europe, and the folks I was responding to sound like they're in Europe.

There's a bunch of various things "kids these days are doing" because of social media and their craving of attention, that are frankly completely stupid and objectively bad, but get them attention due to being obnoxious. Carolina squat, stance, and popcorn tunes all fall into this category. Stance kids in particular /know/ they're doing something objectively stupid and dangerous and respond by putting "locally hated" stickers on their car. There's a lot of kids, especially in the West, without good family life and too much exposure to social media who will do anything, no matter how obnoxious or objectively wrong, to get attention, even negative attention. This is just how it extends to cars. We all hope they grow out of it, because otherwise they're destined to be wastes of the oxygen they're breathing.