As didactic as that comment was, I suppose I could have said grandpa. I did use grandma, however, because I don't personally have any grandpas on my facebook, and in my own experience (and evidenced from this link) there are many more grandmas than grandpas on facebook:
Even then, however, I disagree that saying "grandma" in such a context is really that damaging. Maybe there's some point to this, but it seems unnecessarily politically correct to me.
http://geekfeminism.wikia.com/wiki/So_simple,_your_mother_co...