Yes, but the question was not about your country of residence. If you are an EU citizen, you're allowed to fly to any EU country on a one way ticket even if you reside elsewhere in europe. Let's say that you're a german citizen residing in Italy. By just showing your German passport at check-in you should be allowed to board a one way flight from the US to the UK no questions asked. You are an EU citizen, UK authorities are not allowed to ask you for a return ticket since you have the right to live and work in the UK.

I am actually surprised that airlines are not aware of this! And no, I've never had any problems. I am an EU citizen and once I flew from India to Germany on a one way ticket and had no problems. Similarly, once I also flew from LAX to Switzerland on a one ticket and had no problems either.

However, I hear of a lot of residents of Canada who have trouble travelling to the US on a one way ticket. If you are a Canadian resident you are leagally allowed to go to the US on a one way ticket. And it's the same if you are a Canadian citizen.

I have an HNL-NRT-HNL ticket booked on ANA for the beginning of May. I am an EU ciitzen who is a resident of Canada. Let's see if at NRT they'll let me board my flight with just proof of being a Canadian resident. If they ask me for a ticket from HNL to Canada, I'll ask for a supervisor (even though, I will have one in my pocket!).