Had a good run with nothing really going amiss lately. Had the occasional horn sounded at me for being outside of cycle lanes that aren't safe to use, and for being in primary position where there are parked cars to the left that I don't particularly want to be doored by, but thats just normal. Then this morning I encountered what I thought was just another ordinary bad cyclist. Got as far as turning off to go along in front of the Colleges, so along past Johns, Trinity, Kings, a picturesque but narrow one way street. Just before the turn off theres a cyclist more or less level with me, on the inside, and I could overtake him but theres no point, as there is a bus parked in front indicating right to pull out, has been doing so for a good few seconds now. I slow down to let the bus go and make sure the other cyclist has plenty of room to pull out for a good view of the road, he ignores the signal from the bus and oncoming vans (who are technically turning off onto our road, even though it goes straight on, but our road gives way to theirs), snarls traffic for a few moments and turns right, regrettably the way I'm also going. Shortly after I follow him (after letting bus move out and the vans pass, doesn't get very far 'cos of those vans the cyclist has stopped). Shortly I'm stuck behind/alongside that cyclist, who is stuck behind a bus, which in turn is stuck behind one of those backwards tricycles with child seats on the front (1/2 to 3/4 behind the guy, the road is one way, plenty of room for two cyclists). He darts on to the path on the left to see if he can get past the van, but the pavement is blocked; after 10 yards or so he hops back on to the road, now rather behind me. Slows down a little to be fully behind me, comes out on my right and hops on to the right hand pavement to see if he can get past the van that way. Can't, so hops back on to the road. At that moment, van indicates to pull in to the left parking spot, I had anticipated this (that van always pulls in to that spot) and was heading for the right hand side of the lane, I maintain rate and direction and go past; the guy who was in the process of hopping back on to the road didn't have a great deal of room to do so and couldn't clearly accelerate past me into the space becase he didn't have sufficient control of his bike after coming off the pavement, and I saw no reason to give him any special consideration. So he yelled at me, that I was undertaking him and that its illegal. You can imagine the row we had continuing along the road In his opinion I undertook him, which is wrong. In my opinion he's a low down scum who should read both the highway code and roadcraft before being allowed back out on to the road, he neither knows nor understands the rules of the road with regard to overtaking, pavement cycling, keeping traffic moving safely and freely, etc., and I made my opinions entirely clear on that. Okay, I could have moved over to the left, slowed down, allowed him on to the road from the pavement. My bad. I accept that. But I'm glad I didn't; I'm just not being bullied into changing a sensible road position to make it easier for an idiot to cycle illegally. Undertaking someone on a road and pulling out in front of them, or even weaving inside and outside cyclist traffic, is a pretty awful thing to do. But to be lectured on that by someone who didn't like that I went past him such that hopping off the pavement was more difficult... Well, no, sorry, POBs (meant here as an insult) like him can just f*** right off.