For every cyclist I've seen that does that, dozens of drivers do the same, and dozens of cyclists don't. Don't label the whole based on the actions of a very visible minority.

That said, "weaving in and out of traffic" is legal in many places and called "filtering." The idea is to get to the front where drivers are more likely to see you, cross the intersection without getting run over, and then move to the side of the road to let cars pass. In many cities, they put a special painted area in front of cars at intersections specifically for bikes to enable exactly this behavior.

Likewise for "running red lights," there's also an issue where some lights don't trigger when a bicycle approaches, and many areas have a law that cyclists may proceed once that's clear (usually 60-90sec).

I'm not saying either is what you're describing, just clarifying what laws typically look like so you can distinguish the legitimate, lawful actions from what also frustrates law-abiding cyclists.