Yeah, it used to be that cars made way to people, but now people make way for cars. It's stupid.

I've also been frustrated with some cyclists, especially now that ebikes have lowered the barrier and brought the uninformed masses onto the streets.

Here are the relevant laws in my area, just in case some of it is relevant to what you're seeing:

• stop-light - must stop, but may proceed if the light is obviously not recognizing you (local law is 90sec, but I've seen anything from 60-120)
• stop sign - treated as a yield, which means stop of there's contention, but only slow if there aren't other cars
• sidewalk - not for cyclists, and cyclists must yield to pedestrians if they use it; cyclists should use the road
• bike lane - not technically part of the roadway, and the law states that cyclists should stay within 3' (1m) of the roadway unless there are obstructions; likewise, cars must give cyclists 3' of space, so cyclists will often "take the lane" (be in the middle) of they're not getting that space
• crosswalks - treated as cars (must wait behind) or pedestrians (if crossing the road with pedestrians)

In short, cyclists:

• may use the crosswalk, but must yield to pedestrians (and cycling 15mph would certainly present a hazard and could be ticketed)
• may use the roads, but need to stay within 3' of the edge (not including bike lane of shoulder) unless there are obstructions
• may yield at stop signs and treat stoplights as stop signs if they don't change for the cyclist

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.