This adjective is normally used to describe a fissionable material — such as uranium or plutonium — that is of suitable quality to be used in the making of a nuclear weapon. Over the past three months, however, we've all been exposed to dozens of references to "weapons-grade anthrax," which uses extremely small spores (a few microns — millionths of a meter — in diameter). Their tiny size means that the spores are easily spread and inhaled, which is what makes them suitable to be used as a weapon.

So it's entirely natural that people have taken up the weapons-grade adjective and applied it to more mundane objects. Besides the tequila reference in the above citation, I've also seen weapons-grade used to modify the following things: drugs, salsa, peanut butter, cheddar cheese, punctuation(!?), and, uh, certain intestinal gases, referred to in semi-polite society as "wind."

Using weapons-grade in non-military contexts may be popular, bit it's certainly not new. I was able to trace this usage back over 10 years (see the earliest ciation).

Here's an even older citation, although this one uses a different "pro-gun" sense:

"There was a whiff of putsch in the air this year when GO-New Hampshire restaged its lethal-weapons night. ... Albert Gore Jr., alone among the Democrats, had agreed to attend, ... but although Gore is determined to court weapons-grade voters in the South, he is apparently worried about his image among more moderate Democrats in the Northeast ... and never showed." —Andrew Kopkind, "Guns of February," The Nation, February 13, 1988