There are several reasons why a person may not legally be able to give true, informed consent to sexual intercourse. For example, if the person is not of a minimum legal age to have sex (an age which varies from state to state), the person does not even have the right to give consent. Another reason may be if a person has a permanent or temporary mental impairment that limits one’s ability to understand the implications of the activity to which they are consenting. For example, a person could be unconscious or could be of below average general intellectual function. But another such situation is when someone is intoxicated.
Most state laws say that an intoxicated person cannot legally give true, informed consent to sexual intercourse, even if they say yes. However, this is often an ambiguous standard, as it falls to the other party to determine whether the person that has consumed alcohol is able to think clearly and make a rational decision as to their actions. As such, though it may not be easy to do in the heat of the moment, you must be certain that the person to whom you are making sexual advances is of sound mind, is fully cognizant of the situation and surroundings, and is voluntarily participating during all stages of sexual contact. If you are not, and your partner wakes up the next morning claiming to have been taken advantage of because they were not in the right frame of mind, you could be on the hook legally.
Enforcement in a University Setting
This is a particularly thorny issue for college students, many of whom consider alcohol to be a normal part of social activities. Private university discipline boards are not bound by the same rules of evidence and procedure that state courts must follow, and they are free to set their own standards for their students. As a result, university judicial charges could be filed according to standards that are different from one private school to another. These standards are often spelled out in the university’s code of student conduct. (Although to make the distinction, students at public universities may be constitutionally guaranteed more due process rights).
However, all this said, the reality is that it is very difficult to prove questions of intoxication and consent after the fact. As a result, criminal prosecution in these situations remains uncommon.