Don't be doing that

Tonight at my pottery class, being the safety geek that I am, I advised a student intent on carving a nearly bone-dry pot to do it over the sink: "You really don't want to be breathing in all that clay dust," I said, observing the powdery accumulation on the table and in her lap.

As soon as I uttered it, I realized I had an authentic use of an acquired Southernism on my hands. I plucked it from the air, put it in my pocket, and present it now for you, gentle readers:

Don't + be + Verb-ing.

Try it:

Don't be leaving your coat on the floor!
Eww, gross, don't be licking that!

You can pretend to know other people's inner desires by inserting the verb want after don't, as in:

You don't want to be teasing the cat, he'll scratch you.

A little Googling reveals that such constructions belong to a broader category of be-usage called the habitual be. The habitual be is a way to indicate a continuous directive. When you say Don't be licking that, you mean it's a bad idea, now and in the future, to lick that, so don't do it. By comparison, the briefer command, don't lick that, is a more limited imperitive: certainly you should not lick that, but you don't necessarily need to make a habit of not licking it because, after all, how often is the opportunity to lick it going to present itself?

How the habitual be arrived in the southern U.S. is unclear: it's common in Irish English as well as African-American Vernacular English, among other dialects. And to be honest, I'm assuming it's Southern only because I don't remember it invading my own speech anywhere else in the country.