Bloody hell, touched a nerve there I think ! However in my haste to pontificate I forgot three other key subgroups…
Pushers: Pushers are primarily an above-ground phenomenon, and one which gets my blood boiling every time. They're the ones with prams/strollers/pushers/general baby wheelbarrow fixture, and they're customarily crossing roads. Because of the nature of the arrangement, they're basically holding their baby out in front of them in quite an unprotected manner. The worst example I saw of this was when I was on my way to work at Reuters and this STUPID WOMAN elected to cross the road between two buses (a completely daft proposition to start with), however in order for her to see what traffic was coming, she effectively had to push her pram out into the road. If traffic had been a little thinner I'd have shot across the road and roundhouse-kicked her in the head for being so stupid.
Blockers: these are the people responsible for the “Please allow passengers off the train first” message in the underground, although to a lesser extent they're found in lift-lobbies. They want to get on the carriage, and they clearly want to be first onto the carriage, so they assert their position by standing firm ready to charge on at first opportunity. The trouble of course being that tube doors are a bi-directional aperture… so in order for the carriage doorway to become free to step into, it means the people getting off the train have to empty that space. Blockers, however, have formed an impenetrable human wall which the England soccer team would be in awe of, so you've pretty much just got to punch through. Having a bag to use as a crowd-parting cudgel is often good for this – a lance would be better, but there's not much justification for having one in the Underground. It's weird really – if you heft a bag in front of you and charge forward, people will generally get out of the way ! But if you're sporting naught but a shoulder-charge, they'll stand there and wait to take it. Maybe they're all short sighted, and having the bag out front is like waving something in their available field of vision to warn them that you're on your way ? There again, it doesn't seem to work for fat blokes or chicks with enormous hooters, so maybe there's more/less to it.
Lemmings: Another above-ground group, which I've come to observe mainly on the chaotic crossing system between Victoria Station and work. At intersections it's a basic law of nature that there's always someone who ignores the little red man and decides to dash across at a gap in traffic. Lemmings however are so wrapped up in whatever it is that's putting their miniscule amoeba-linke minds through their machinations that they don't bother to look at the red/green men, but nor do they look up to examine for gaps in traffic. They just think “Oh, someone's crossing the road – it must be time to cross the road !”, and step out into the wild black yonder with a half-dazed look on their dials, customarily to be jolted back to reality by the hooting and rapid appearance of a bright red bus-front into their narrowly focussed peripheral vision. I find Lemmings particuarly stressful, as having spent several years doing first aid training and being a generally helpful member of the community, I know that I'd feel compelled to offer assistance should one of them come unstuck, but of course one only wants to have to do such things at the site of a genuine accident (like the time I had to give the bloke CPR on the corner of Greenhill and Glynburn Road on the way to work one day), not because some asshat didn't have the presence of mind to pull their head out of their date and look about them. You've only got to look at any sports blooper/outtake video to realise just how fragile our water-bag bodies are, so to indiscriminately hurl them in front of high-velocity metal projectiles seems to smack of indications that we really don't deserve to be at the top of the evolutionary ladder, and maybe we're sliding back down again ?