[morzh]

Well, if we keep bartering, so he does not even have to know what B+ is, he is safe to deal with.
Or, maybe he cannot tell the difference between + and -, and so keeps putting B- to the chassis, and this is safe.

But even if he ever learns it, I am still safe, as I always plug his radios through my isolation transformer

So, Kirk, you will have to come up with something really devious. Like a live mouse darting out of a chassis...or your photograph with a big grin and "gotcha!" print.