Had someone Infront of me doing 40 in a 60, then 35 in a 50. Imo that's driving dangerously, so I overtook before they caused a crash (they also started braking for a roundabout about half a mile away (while travelling at 40).
I figured they would be the type of driver to slam on instead of indicating first.
Exact same thing. Then they wave their arms and speed up when overtaken.