I don't think there's any way to discriminate between crazy things your mum believes and crazy things the man on the street corner believes.

I also think the virulence of a meme complex, like the virulence of a virus, is very dependent on the context i.e. the population it is introduced to and the other memes it competes with in that population.

"what do you think you know, and how do you think you know it?" is snappy enough to be "virulent" and, I think, not too harmful to the individual host.