Earlier this month I was waiting for check in in LIN when a mid age Italian arrived and tapped on my shoulder telling me I was in the wrong line. He said: "you see? This is only for frequent flyers like me". He was indicating the oneworld gems and I promptly asked him which one he had. "The red one, you have to fly a lot to get this one".
At that point I said: "oh I see, well congratulation but I have the blue one and I fly CE so I'm perfectly allowed to use this queue, never judge by appearances".
I'm 19 years old and my age might confuse a bit, but I find ridiculous that a person comes and tell you you can't stay there based on nothing.