Sex should not be merely a question of whether a person innocently says yes or no but more of a societal thing. Let's be honest, who really cares about some bimbo's opinion, or even some highly-educated British man's opinion. Rape is about politics. I think it is ridiculous to assume someone would care about whether you consented. Rather other people's opinion is what seems to count. I think consent is when a woman abuses you. If a woman calls you “gay” or “a virgin” that should count as consent to sex as it is “incitement to sexual intercourse”. If someone treats you properly and says no to sex and can give a rational enough explanation for the decision that might stand up in court?
It's probably safe to assume that someone isn't interested [in sex] if you haven't already had sex with that someone and they enjoyed it.