One thing that might make a difference here is how subjective "the boss is acting like a huge turd" can be.

If almost everyone would agree on the turdishness given a couple of facts on the case (none of this "heard from a friend of a friend" bullshit) then discussing and raising might be possible (though I'd probably still just leave).

But if people's assessment of the truth of that statement will depend hugely on that network of beliefs and values called "worldview" as well as exposure to different facts on the subject... then it's going to be hard.

It is allowed, but your boss is also allowed to fire you. Ianal

It'd be a foolish thing to discuss openly.

Is it at yours?