Admittedly, this has been for the most part a semantic argument, but clearly one that many of us feel strongly enough about to keep the dialogue going. It seems that there are some who believe that performing a design activity qualifies one as a "designer", no matter how infrequently or successfully. I believe this is a matter of interpretation, and I'm willing to say why I think that interpretation is flawed.
But first, here's what I think a "designer" is.
A designer is one who performs design activities as a primary part of his or her vocation or profession.