Quite niche this one, but people who are driving through Dyfatty lights from Hafod direction, with the intention of turning right onto Carmarthen Road. The ones who don't bother going right up to the stop line at the end of their lane, often leaving a good half a car's length gap.
They either don't know or don't give a shit, but it often causes traffic to back up behind them and it causes chaos because it blocks two lanes. I'm more commonly found in the middle lane which is right next to it, but it pisses me off so much I've recently taken to winding my window down, pointing at the line and saying "that's where you should be".
Selfish and inconsiderate twats.