The radio talk show host went in on the Brits for putting on such an extravagant show for their new monarch -- who was officially crowned over the weekend in what amounted to a 3-day celebration, capping off with a massive concert with a lot pomp and circumstance.

You figure that's exactly what a coronation calls for, which HS says he understands -- but at his core ... he finds the idea revolting, seeing how they're pouring money down the drain.

Howard also takes some personal potshots at Charles himself ... saying the guy is no war hero, even though he kinda gets treated like one anyway by his royal subjects. His cohost, Robin, was getting in on the dogpile too ... and they called out Queen Camilla as well.

The 'American Idol' moment -- in which both Charles and Camilla made cameos on the show -- was in their crosshairs too ... with Howard saying they looked like complete stiffs on there.

Howard's gripes seem to be steeped in what a lot of people -- particularly Americans -- say about the monarchy ... namely, that it's outdated and completely unnecessary in modern times, both in terms of reverence paid and the money spent to showcase the Royal Family.

He says he gets its tie to tourism and that it drives interest in Britain at large, but the dude's completely unimpressed by the institution  ... and definitely isn't a fan of HRH, Chuck.