I mentioned on another thread that I have sung karaoke once or twice (the first time I sang, I did "Nothing Rhymed", which is a song Roger raves about).
My point is, very often people smirk, or laugh out loud when I perform, even though I am usually note-perfect, sing with dignity, and dress smartly. I always consider that to be very rude. In fact, when I was doing the lovely song "A Single Girl", I came quite close to actually walking off the stage.