To MBSLynne above - of course I sit there quietly and listen to the awful singers of very, very long songs. I suppose that if I was more courageous, than I am, then I would tell them what I thought. Trouble is, how do you do that without hurting their feelings, putting them off singing for life or getting hit?
I still think, though, that being a good singer (especially in a singaround situation) is about more than just singing your longest song whenever you get the opportunity - but about having good taste, understanding your own limitations at any point in your singing career (whilst, of course, working hard to overcome those limitations) and having regard for the feelings and patience of other people in the group (especially the organiser, who wants to give everyone their turn).