Critical Ass
This is a point where you are partaking in anal sex and it is a definite problem because the motion of thrusts has produced a plunging effect and now shit is about to spill out in an amount that can accumulate a small or lage pile. When it just already is spilling a little that is also critical ass as this is most commonly how it is reached. I am implying that it doesn't have to be a point where the person receiving the thrusts feels it about to come out or the person thrusting feels an approaching barrier that is progressively preventing more room for penetration or it just begins to feel really mooshy. Those are also critical ass. This is the point where the person receiving the phallus has to inch one self over to a safe receptacle with out letting open the flood gates. It can become a spout to where the person is really taking a full-on dump and not just a spill.
Matt:"Oh no... do you smell that? Oh there's too much grease on the penis now."
Kate:"Oh it's fine...pfffrrrohht. Actually... I think we have reached critical ass."