Consent may be given expressly; it may also be implied from custom, conduct, or words, or by law.
If consent is given by mistake, it is still a good defense unless defendant caused the mistake or knows of it and takes advantage.
If the consent is induced by fraud, it is not a good defense. However, the fraud must go to an essential matter.
Consent obtained by duress is not a defense. But threats of future action do not constitute legal duress sufficient to invalidate express consent.