Not to mention if that if somebody needs to come over, the proper thing to do is signal first. Then I'm happy to politely ease off a bit and open more space for them to come over safely.
It's the people who aggressively slide right over just a few feet in front of me (cutting off nearly all of my safety buffer) without so much as a signal that really drive me nuts.
It's the people who hit the gas when they see your signal, that really irk me. In Austin I stopped signaling because it was a punished behavior.
My experience driving in MA and NY was similar, but so often it was because a rusted out shitbox was trying to merge in that would slow down traffic significantly, and not only put me at risk of rear ending them, but being rear ended myself.
When flows merge, there's turbulence. There's less turbulence if the flows are more closely matched, including speed.
Unless I'm the last car in a line and there's plenty of open space behind me. Then you should just wait until after I've passed before merging, because otherwise you create a little ripple in the flow. A few ripples and you got a wave, and that's how you get traffic.
So for the love of gods, if you're merging, even if you signal, match speeds for merging. If you're too slow to match speed, then suck it up buttercup, and hang out in the right lane until there's an opening.