I've unfortunately used "spaz" before remembering what it can really mean.

I don't think people mean to be offensive either - they're words that entered our slang. Though there is a "macro" per se that actually does use mental retardation in an offensive sense - "winning an online argument is like the special olympics: you're still a retard." The macro is of a boy with Down Syndrome running. Though even then, I don't think people mean to degrade people who are retarded... they just don't think. And if I hadn't worked with special ed kids in high school and seen the effects of "retard" firsthand, I probably wouldn't either.