Yeah, I'm familiar with Rationalist Taboo, and I was looking for a substitute for "politically incorrect" fitting the description provided. "Taboo", in its sense of "culturally forbidden" rather than its sense of "party game about avoiding words", is what I came up with. Sorry if that lacked clarity.

There are several reasons to play Rationalist Taboo, though; I'd assumed that the grandparent wanted to drop the phrase mainly because of its political loading (which seems to be causing some problems here), not because of any implicit assumptions or ambiguity of definition that needs to get aired out. In which case brevity would be no sin.