From a UK perspective:
1. Driving below the speed limit is acceptable provided it isn't TOO slow. What is too slow? Depends on the situation and conditions, but it's a speed slow enough to present an obstacle and hazard to those around you. If someone's doing 25 in a 30 then it's acceptable even if it is irritating when there's too much traffic to overtake them
That's why it's called a speed 'limit' and not 'target'.
2. Driving slowly in the overtaking lane when others are around is just dumb and I hate those people too.
3. Some people can't afford much better
4. If it's a double lane highway and the overtaking lane is empty I have no problem with this, you simply move over to help them join the carriageway. I've noticed on many videos, situations where someone gets mad at someone pulling into their lane when there is a perfectly empty lane to their left they can simply move into to 'help' the turning vehicle out. A large cultural difference between the UK and US is where our traffic is more co-operative in helping each other merge onto a fast road, people in the US generally seem less inclined to want to share space with each other, it's almost like "it's my lane, I shouldn't HAVE to move for you!" kind of attitude. If however the left lane is busy then yeah just merging on is a dickhead move as it forces you to brake with nowhere to go. I'm not referring to last-second pull-outs, of course, as that's clearly insane.
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I'm not denying that, and indeed the majority of drivers believe they're really skilled and good when they're deluding themselves. But at the very least the fact the OP acknowledged many common bad driving habits instantly tells me s/he is more 'clued in' and 'aware' than most of the autopilot morons you meet out on the road. Yet you tell the OP they're the "most dangerous type of driver out there"? Sorry but I think the more dangerous types are the ones who simply don't CARE. My dad for example is an awful driver and he's fully aware he cuts people up, tailgates, etc, and he does it on purpose to try and bully other road users to let him go by. Are you SERIOUSLY telling me the OP sounds more dangerous than that? Telling someone you don't even know that they're dangerous simply because they are implying they're better than most after a year's experience, is a bit unfair, no? You need hard evidence to accuse someone of being dangerous.