I had a couple of em.

Most embarrassing... Honda Civic 2nd Generation back in 1982. Even the Datsun 120Y, which i had prior, looked nicer.

Most troublesome... 99 silver Rover 400 limited edition (factory alloys and spoiler). Why in heaven's name did i even buy that piece of junk??? At that time, it really looked like a well-kept car. Clean as a whistle, low miles, one owner, and cheap. Guy said gasket was done, so good for some time, i thought. Two months on, cruising with gf and 2 dogs along the scenic route around Lough Derg. A distance away from Killaloe, in the middle of no man's land, passed by a lady whose car had broken down. Not even 30 secs after turning a bend from her, the feckin Rover just conked out, died, kapoot. Luckily had breakdown assist. Waited 40 minutes, nice tow-man came & hoisted the bleddy thing back to friend's garage in Limerick. He could not locate the fault for a couple of days. Eventually got it running with damages to the tune of 300e. Then the gasket blew, and started producing cottage cheese inside the engine. Replaced the engine, and it was fine for a while. No problems at all. Then the big freeze came, when was it, '09? Cant recall exactly. Left the car undriven for a few days, and when the snow cleared, found that the car would not start. Towed it to another friend's garage and he found that the engine sump had cracked from the cold. Sickened. Still, i got 150e for it. The body/interior/ac was in very good condition. My buddy put in a new engine and sold it on for 600e. Still see the car around the odd time when im in Limerick.

Second most troublesome car... a 02 Bmw 318ci. Lovely car to drive and all, but never-ending maintenance. Unlucky i guess.