>So what's the PC word preference for "stupid" one that's not demeaning to other groups but one that is forceful and shows disgust?

fortunately(?), there is no dearth of words for the concept; here's a selection from Merriam-Webster:

SIMPLE, FOOLISH, SILLY, FATUOUS, ASININE mean actually or apparently deficient in intelligence. SIMPLE implies a degree of intelligence inadequate to cope with anything complex or involving mental effort <considered people simple who had trouble with computers>. FOOLISH implies the character of being or seeming unable to use judgment, discretion, or good sense <foolish stunts>. SILLY suggests failure to act as a rational being especially by ridiculous behavior <the silly antics of revelers>. FATUOUS implies foolishness, inanity, and disregard of reality <fatuous conspiracy theories>. ASININE suggests utter and contemptible failure to use normal rationality or perception <an asinine plot>.

or, one could resort to this infamous internet rant:

"Sir you are an apogenous, bovaristic, coprolalial, dasypygal, excerebrose, facinorous, gnathonic, hircine, ithypahallic, jumentous, kyphotic, labrose, mephitic, napiform, oligophrenial, papuliferous, quisquilian, rebarbative, saponaceous, thersitical, unguinous, ventripotent, wlatsome, xylocephalous, yirning, zoophyte."

or, we could just invent some tsupid new word...