If he continues, after she has made it very clear his advances are not welcome, it is considered – rightly and in law – sexual assault and that man is subject to arrest and criminal prosecution.
Consent is also demanded – in law – when it comes to most contracts. You cannot legally be bound by a contract you never signed, nor by one which you were forced to sign – because duress obviates consent.
But the government tells us we must "consent" – or else. Also that our "consent" is implied – whenever it suits the government.
In our cars, for instance.
The doctrine has it that because we asked to be allowed to drive on the government's roads ("public" isn't an accurate term; ownership is a function of control. The government controls the roads and therefore owns them) we have given our "consent" to all sorts of things – including being forced to prove ourselves innocent of crimes there's no reason to suspect us of having committed.