This will always be a problematic area both within airlines and universities.
The interpretation in English law over ability to consent is a nightmare. For example if a bride gets drunk on her wedding night, can she consumate the marriage or would that be rape.
I feel in law, it is impossible to judge if the person was 'capable' to consent, other than on the balance of probabilities, which only applies to civil law.
Having said that, I feel that there are some people who think there is a presumption of consent if someone invites you back to their room or share a bed. I think we need a little more education here for cabin crew and pilot training regarding consent.