It isn't someone else's responsibility to set our limits. Each assumption about your partner's intentions or receptivity that you make and act on is a choice that you are making. Relying on our optimistic reading of our partner's body language is a good way to set ourselves up to commit assault. Sex with someone unable to consent is sexual assault. Sex with someone drunk, stoned, asleep, passed-out, retarded, underage or otherwise unable to consent is sexual assault.
Consent is a verbal process, established without coercion.
Here is what it means to me. These are but a few examples of questions that help establish that both parties are equally interested in participating. If someone, female or male, feels assaulted they have been assaulted. After the fact is too late to find-out for the first time how our partner felt about the sexual interaction. Someone can change their minds at any point.