On the way home today I was behind a colt in an 80 zone who was doing 60.
All the bends are on hills so every time we came out onto a straight he sped up coming down the hill to around 80 and then slowly went back to 60, and thanks to that I had no opportunity to pass even if I ignored the speed limit because of occasional oncoming cars.
He was also drifting all over the road. When we finally reached the end of the road and turned off it becomes 2 lanes, so I calmly came up next to him and gave him the look. He didn't even notice (and was holding his roof handle thing with his right hand and steering with his left?).
So I dropped it into second and... Departed

I didn't speed though, it was 80 still
Being slow is one thing. Being inconsistent is bloody infuriating.
I've seen a woman with children in the car do the same thing before, only she was actually crossing over double white centre lines. This is a road that is frequented by large trucks. She then started braking (before indicating) and indicated to turn right maybe 3 seconds before she stopped to wait for traffic, while still with 2 wheels over the centre line.
This was just over the crest of a hill in peak hour traffic as well. She had at least 5 people behind her.