I'm not terribly polite if they are coming right at me. I usually hold my line (unless I'm putting them in danger, then I do my best to move to the right and make room) and say this loudly, "You're on the wrong side!"
I take a similar approach.
Wrong way riding bothers me the most in a bike lane on a busy street, such as Halsted through Boystown. More than once I've given someone an earful in that area. "Hey, these bike lanes are ONE WAY. There's a lane on the other side. Use it!"
Ooo I like this technique.
That's good to know it's not just me. I just slow down closer to the right since they can see the traffic anyways.
Having once been crashed by a salmon, i became much less tolerant or polite. i once deliberately elbowed one while passing (i'm not that aggressive anymore.) If there's room, i'll go to the right and force them to either pass me to my left or stop altogether.
MAJOR peev. Among other reasons, these ball-less wonders (sorry, ladies) can't handle riding WITH traffic because they're afraid of being "blindly" hit by a car from behind. No reasoning with these knuckleheads that a head-on collision with an automobile is MUCH worse. What takes the cake is their default assumption that any other cyclist they encounter who is traveling WITH the flow of traffic must veer into traffic to accommodate them, looking back over the shoulder all the while managing not to collide with Wrong-Way Conway.
Held my line once a couple of years ago on Stony Island and the oncoming cyclist just plowed into me and STILL wouldn't budge after we had crashed. He was monosyllabic with dead eyes and was fairly seething with unfocused hate. He kept growling, "I don't have time for this." Some shoves were exchanged. I sized him up and concluded I wouldn't last very long in a fist fight with this particular opponent (significantly younger with more upper body muscle mass and seemingly no reluctance to use it.) I also was mindful of my "new" Litespeed and his piece of shit beater bike, and wanting to protect my baby, I grudgingly moved aside to allow him to pass.
Thankfully, I've never had a collision with a salmon-er but have had a few close calls. What I do is directly related to quick risk assessment of the situation, (I.E. rate of speed, amount of traffic, size of moron, etc.).
Sometimes I yell well before we meet. Sometimes I glare and bark angrily as we pass. Sometimes I stop immediately as close to the parked car as possible and utter obscenities through grit teeth.
Ride defensively, always have an escape, and never allow anyone to put your safety at risk.
If one decides to ride the wrong way they are taking responsibility. This is the case whether they have the cognitive ability to realize that they have taken responsibility or not. I will not move for somebody riding the wrong way unless my refusal to move puts somebody else in jeopardy. We have all had times when we have felt forced or made a conscious decision to ride the wrong way for a short period of time. When we do so we know that we are responsible. We must be considerate. We are interlopers. So, when somebody else does this I insist (I don't assume, I insist) that they take that same responsibility. If the knucklehead coming at me is in danger it is unfortunate, but it much better than me or the poor kid standing nearby be in danger. The only caveat to this is that if there is safe room within a lane or if I am on what I know (not assume) to be an empty street I will veer over to get out of the way just as I will veer to get out of the way when I am walking on the sidewalk towards a disheveled person who is muttering to himself and gesturing emphatically while wearing a winter coat on a 90 degree day. I'd rather not engage. Assuming it is not safe to veer I am, as others have mentioned, loudly (and perhaps as crazily as the guy with the winter coat) letting the salmon know that he is going upstream and that he is going to get filleted if he continues to ride and as we get closer I will be shrieking to the point where bystanders will be thumbing a 9 and a 1 and a... on their phones. Most fish get the idea.