I don't know what it is about cyclists that provokes such venom (Well, I do actually), but some people have it in for them. It's probably, as has been mentioned, their selfish, holier than thou attitude.
Where I walk the dog in the morning, there is a lakeside path surrounded by woods. Cyclists are not allowed on the path, but they ignore this. Because they are not allowed on the path, they think the woods belong to them, and take great delight in charging past people on muddy tracks, ringing their silly little fairy bells and barely missing people (and dogs).
Every morning when I walk in the woods, people have gone to a great deal of trouble to put large branches and even small trees across the paths, no doubt hoping one of the two wheeled terrorists will come a cropper. For folk to be bothered doing this, they must be really pissed off, it takes some effort by the look of it.
I must confess, if one of them went a bit too close to my dog, I think I would probably kill him.
Dogs are another pet
hate of some people. They have to be kept on a lead on the path, but dog owners ignore this. There are signs threatening huge fines should your dog shit on the path and you fail to pick it up. As there is no one to enforce this, there is dog shite everywhere. Cyclists must get this stuff all over the bike and themselves when illegally cycling through the illegal dog shit.
Children are not the favourite type of human for a lot of older couples who walk on the path. Noisy little beggars spoil the peaceful walk with their shouting, screaming and running around. Shouldn't be allowed anywhere near. Old people are generally disliked by everyone. Moany old bastids.
So....that leaves young, childless couples who don't own a dog or a bicycle. But I'm sure someone must hate them too.