There's a street near where I live which is one-way. It has cars parked on both sides, just space for one car through the middle, and a blind turn off to one side, so you can understand why it is one way. I have before driven down it (at 20, which is the limit, or less - often more like 5 or 10) and found a cyclist coming the other way at speed, often turning in at the end. It is really scary. You do not have much time to see them and slam on the brakes. I do honk when they do this (if I have the time to react), because plainly they haven't seen me (and don't know it's one-way).
Today, three cyclists came riding triple-file down the middle, the wrong way. I slammed on my brakes and honked, and because I'd come to a complete stop and my window was open, I called 'it's one-way!' to them.
One of them laughed, and said:
'Don't be stupid - I live here! It's only you who honks!
I said it's one way and it's illegal what you're dong.
'I don't think it's illegal! It's not illegal. No-one cares! Do you know what speed limit it is?'
I said 20, and I hadn't been doing 20.
'Oh, I think so, I think you were.' (I wasn't. I wouldn't have been able to stop for them if I'd been much over 20, which is why I wasn't. I'd been doing mayb 5, because another bike going the right way had been in front of me. He seemed to find all of this very funny).
At this point one of the others slammed his hand on the back of my car. They were all laughing and shouting.
Ok, I know probably it was pointless to stop, or to argue. I am still shaking.
What can I actually do about it? They obviously either don't know, or don't care what the law is. One day they are going to get themselves killed, or me, or some other driver, killed.
I don't have the first idea what to do but I want to do something.