The opposite of a wizard in the Harry Potter books, a muggle is someone who cannot do magic.

This has been appropiated for use with wizards of a different kind: the demon programmer. A quote from stephen, posting at The Rob Malda Rule at perlmonks.

When you're dealing with nonprogrammers (Muggles? Trivial persons? :) ) it's best to be armed with charts. Nonprogrammers will occasionally panic at screenfuls of text, but they often feel at home with pictures.
I wonder when this will enter The Jargon File?

Oops... I swear I didn't write it this way (my memory isn't very good, though), but this originally had Rob Malda listed as the person who came up with this quote. My bad... I apologise enormously...
Just something else I found... This, for example, from Hearst's American Magazine of July 1937:

An entire family was murdered by a youthful (marijuana) addict in Florida. When officers arrived at the home they found the youth staggering about in a human slaughterhouse. With an ax he had killed his father, mother, two brothers, and a sister.

He seemed to be in a daze.... He had no recollection of having committed the multiple crime. The officers knew him ordinarily as a sane, rather quiet young man; now he was pitifully crazed. They sought the reason. The boy said he had been in the habit of smoking something which youthful friends called "muggles," a childish name for marijuana.