Mine is definitely the trend of doing “catless downpipes” and “resonator deletes” making your exhaust super raspy as a means of gaining more volume rather than doing a proper exhaust setup. Especially since high flow cats these days will flow more hp than most are making.
It’s not necessarily my least favorite, but the people who intentionally rewire their CHMSL to flash when braking just annoy me. It’s illegal where I am and makes them less easy to identify at a glance as braking. My actual least favorite is the stupid bro dozer coal roller type vehicles, largely because they’ve tried to gas me multiple times before