at traffic lights they cut to the front, 
    only to advance relatively slowly when the light turns green

    they blow through a stop sign as a car is approaching

I thought the former was entirely proper -- motorcycles do similarly, going up the gap between traffic. The latter, though ... I've seen that far too much, and is frustrating.

I also see kids and adults riding their bicycles on the sidewalk, sometimes even the wrong direction. I used to get mad at that, until I realized that our local cycling infrastructure is crap, and _on that street_ I'd not want to cycle on the road either.