How can you prove consent?
The same way you do so with any other legal contract - have the agreement signed and notarized.
That sounds like a joke but it's the logical conclusion of making 'affirmative consent' a legal requirement.
I think I've said it before here but I think the root of the problem with the 'rape-culture' mentality (the SJW idea that we live in a culture that condones rape and sexual violence against women) is the conflation of behavior that is currently accepted in modern liberal society (the hook-up culture, sex before marriage, guilt-free sexuality) with behavior that is not accepted - such as non-consenting sex.
Hence we have a situation where a scenario that should be unremarkable - for example a young man meets a young woman at a party, have fun and decide to have sex - is viewed as being in some way inherently wrong.
To me it appears that the underlying assumption on the part of SJWs is that the behavior is wrong but there seems to be a need for them to rationalize this using other, much more rapey, words.
The man isn't simply attracted to the woman, he has a sense of 'entitlement to sex' with her.
The couple don't simply mutually fool around, eventually ending up having sex, the man goes ahead and has sex with her without asking for explicit affirmative consent.
The couple aren't simply enjoying the party and easing their inhibitions using alcohol, what's happening, in fact, is that the man is plying the woman with alcohol to make her incapable of informed consent to any subsequent sexual actions.
There is a weird synergy between the SJW demonization of normal heterosexual behavior in the West, and the wishes of those of extreme conservative or religious fundamentalist thinking. There's not a complete agreement, of course, but there is a significant overlap in that both groups essentially want to end the current situation that they both regard as sinful or wrong, albeit for different reasons.
If we disregard the idea of a legalized notary signing off on all requests for physical interaction between a couple where are we left?
We either have a situation where all interactions should be video taped in case of future disagreement over what occurred (a somewhat sleazy approach which, however, has
managed to save more than a few men who have been accused of rape), or we start to accept the idea of a witness - a chaperone, if you will - who will provide an independent testimony regarding anything that occurred on the date.
Nothing I've mentioned so far seems practical and yet even if we agreed on one of them it wouldn't affect a major hole in the entire premise of protecting women using 'enthusiastic consent' provisions. That hole is the fact that consent is not something that solely arises in first date scenarios. Consent is something that is required on both a first date and after fifty years of marriage.
SJWs like Lacy squeaky Green may get all hot and bothered by the idea of a guy asking for permission to kiss her on a first date but I suspect she'd get pretty bored with it if he kept doing so for for years afterwards.
But shouldn't he be required to keep doing so in perpetuity?
Surely he must.
And not just for kissing, for every aspect of sexual interaction.
Now I don't discount the idea that there may be some people that would go along with this and perhaps even enjoy it, but I suspect we are straying away from the idea of protecting women and instead wandering into the territory of uncommon sexual kinks.
Normal sexual behavior is predominantly based on unspoken body language that is used to convey implicit consent. Any misunderstanding of this body language (which must happen frequently) is better combatted through the use of assertive language that conveys non-consent rather than the other way around, explicit enthusiastic consent for every interaction.