From a personal perspective Audi drivers have taken over BMW drivers in the last few years as the most irritating, just when Audi has gained a bigger share of the fleet car market....but round my way the worst by far are the (not so) yummy mummies driving oversized and over specified SUVs/4x4s dropping their little darlings off at school on the way to the tennis club or gym.
Agree re Audi. Watching The Chelsea Tractors being parked by Yummy Mummies is certainly an experience.
Not to rope every Bmw driver into one category as obviously a few will be ok..... My wife and i have our own reading of the vast majority of them Bloody Massive W**kers