I really hate:
1. Cagers who intentionally block my progress.
2. Cagers who, when trapped in traffic queues don't look before jumping into that gap that's just appeared in the lane on the other side of my filter line.
3. Police speed traps on the A13 that cause the traffic queues that endanger my health and bike.
4. Scoots/bikes filtering behind me with their headlight on full beam. "Yes, as well as all the cagers I can see you mate and I'll pull in when I get the chance but I can't see s*&t ahead of me, thank you very much you tw*t. In the event that I miss something appearing in my path please sign something to say 'yeah, it was my fault she was blinded'."
5. Cagers who just don't look.
....I'm sure there are more... just can't think of any more right now.