the question wasn't should we not apologize if we lash out, or even should we lash out. The question wasn't should we or shouldn't we treat our T with courtesy and respect and compassion.

The question was, shoud we feel guilty when we are not nice to our T.....

if we are just ***holes in general we won't stay in therapy anyway.
If we are not just that, and the lashing out, the wrong perception, the trigger, the whatever you call it, is a case of negative transference, don't think for a minute that it is just left to lie there like that!! It's a tool, as we discussed elsewhere; the T can use it to show the person their behavior pattern; to help the client trace it back tothe source; to help the client form a better reaction for the future.

So shoudl we feel guilty? If it's due to transference, I say definitely NOT. Because my T says not.
Should we apologize? I say definitely YES. and I know from plenty of experience that the guilt will set in anyway, and shame too, and you just have to own it. I think the T really wants to hear you say, "I know, it's not about you". that is (at least in my case) progress in therapy.