I can talk about drivers that would gladly let you crash at the end of the on-ramp rather than let you merge, not changing their speed one bit so they either have you crash at the end of it, or slam the brakes then be forced to merge in from a full stop while the next guy is coming at 80mph.
Not that bad on highways, but a real thing on parkways. I cut these off mercilessly.
Of the many things I was adamant about when I was teaching ghe little one to drive was this. If you see someone on the on-ramp - you help. You can help them by slowing down to let them through, by accelerating to let them behind you, or by getting to the left lane if there's no one behind you.
And points off every time I see you driving along some other vehicle for no good reason. Even if you're on two separate lanes - don't stay in the same lateral plane. Assume that next thing that'll happen is that car going to end up in your lane for no good reason.