We loves it below the line, where we can, apparently, post about the trio of topics verboten in the workplace, viz., sex politics and religion.
the banter and wit @ mudcat is often great fun & a terrific timewaster. Let's keep up the witty bits whilst answering the OP in the great ethnographic folkloric tradition if this place. My post above, essentially equating aitch with eta, was an aha of mine of a few years back, though it's simply a hunch lacking corroboration of any kind...
Anyhoo, while thinking of a few hundred 'h' words to follow up on Laura , EdT and others, I noted we'd already covered sex, politics and religion ~ I think the expression is exclusively uttered as an expletive. ¿Does the interpolation of the aitch perform some magical function which makes it 'not cursing'?
aaargh...back to me bowlback mandolin. Await folklore feedback and a bunch more heterodox suggestions...

keep on pickin'
dennis