The times I've done it were for:

• One guy who had his phone in his steering wheel and was playing some sort of online gambling the whole drive and didn't look directly at the road once
• One guy who was driving around on a spare tire (doughnut) on the highway at speeds way above those it said on the tire.

I mean I can look the other way on just about anything (I've given 5* to a lot of questionable driving decisions and shitty cars) but when you are putting my life at risk, that's where I draw the line.