Ask when sober, plain and simple. Always stop when there is even a hint of withdrawal of consent or willingness. Too drunk to drive, then too drunk to give or receive informed consent. Hmmm, maybe lovers should have a designated what, referee, lover, chaperone. Might have stopped some people from some painful mistakes. I treat sexual offenders, many of whom failed to follow the basic rules of consent and ended up creating a victim and landing themselves on a nasty social registry.