Are you a man about to leap into bed with a woman, worried that you might not later be able to prove in court that you’re not actually a rapist? Well now there’s an app for that – or rather, there was.

Good2Go was launched with great fanfare last autumn, offering to provide users with recorded proof of sexual consent that could be produced in evidence if necessary. All a man had to do was get his partner to type the answers to some simple questions – including how drunk she was – into his mobile phone, and the app would confirm if it was time to dim the lights or hastily replace your trousers. Proof, cried the critics (if proof were needed), that sex will shortly be reduced to a joyless contractual engagement for those few men brave enough still to risk it.

Except that Good2Go was a disaster. The app was pulled within weeks, not just because men hated the idea, but women did too. If you’re not intimate enough with someone even to talk about sex – if it’s so awkward that you have to negotiate through a screen, with all the profound emotion of getting money from a cashpoint – how could you ever actually do it? Nothing could be further from the way couples in real life operate – namely by paying attention to what their partners are doing, saying and feeling.

All of which helps explain why today’s furore over new guidance from the Crown Prosecution Service – making clear that alleged rapists who say the sex was consensual should be asked how they knew she was consenting – is overblown. As the director of public prosecutions, Alison Saunders, made clear, it’s just clarifying what police and prosecutors should be – and often are – doing anyway. Nobody is being asked to “prove she said yes”. (The legal test has long been whether it was reasonable for a defendant to think she consented at the time; any reason he had to think she did has always obviously been tested in court).

The presumption of innocence until proven guilty is not at risk, any more than it is when police ask a suspected bank robber who claims to have been home watching telly at the time of the offence to name the programme they were watching. The law hasn’t changed. The sky hasn’t fallen in.

And what it absolutely doesn’t mean is that nobody can ever have sex again without written permission. Women don’t want to start ticking a box to agree terms and conditions any more than men do. They’d just like men to notice, and respond appropriately, if a woman is kicking and struggling and saying “stop”; or is frozen with terror; or is comatose with booze; or is, in any other way that would be obvious to a reasonable human being, not up for it. This does not seem a massively burdensome ask.

Some will say, of course, that women just don’t understand men’s fear of being falsely accused – vanishingly rare as those cases are – or of what seemed to be an ordinary, if drunken, hookup coming back to haunt them; of getting mixed messages, and reading them wrong. Perhaps we don’t. But like all mothers of sons, I have an interest to declare here.

Thankfully all this is many years away yet for mine; but watching friends with teenage sons worry over what to say about girls – how to counter the warped ideas about female sexuality conveyed by porn as well as the age-old playground myths – puts things in a slightly different perspective. And the single most practical thing I’ve stored away for later recital is the message increasingly dished out to male students on American campuses: don’t look for consent in a sexual partner, because that’s too low a bar. Look for enthusiasm.

It’s what was missing, in spades, from that soulless app: enthusiasm, the unmistakable sense of not being able to keep your hands off each other. But it’s also what is missing in all those cases of young women paralysed with fear, or barely conscious, or struggling and sobbing but eventually submitting because they’re afraid of the consequences otherwise.

The trouble with looking for consent is that it’s too easily confused with well-she-didn’t-exactly-say-no, with being too plastered to fight back, with wrestling someone into submission. Enthusiasm, on the other hand, is harder to mistake for anything else. And if it was there, but suddenly evaporates – well, you could always ask what’s wrong. If those two words kill the mood dead, it almost certainly wasn’t the right mood to start with.

This difference between enthusiasm and submission can be taught surprisingly young, long before the mechanics of sex itself. What’s lost in tabloid outrage about sex education for the under-sevens is that at this age they’re not learning about the birds and the bees, but about how platonic relationships work: about respect for others, not bullying or forcing people to do things, realising you needn’t agree to something that makes you feel bad.

Even a child this age can begin to grasp that a rough-and-tumble playground game is only a game if everyone’s enjoying it, and that if someone’s being picked on then it’s no longer a game.

The “affirmative consent” programme in Californian universities (which makes clear that the absence of a loud no shouldn’t be automatically interpreted as a yes) is, as its tutors point out, based on social skills they’ve had since they were kids: the knack of refusing and accepting refusals with grace, the ability to read other people. The child who is utterly impervious to other children’s feelings at seven – who doesn’t care whether they want to play rough or not – is the one to worry about at 17.

What women find hard to understand about the sort of rapists who claim they’re not rapists really, just normal men who misjudged things in the heat of the moment, is precisely this glaring indifference to enthusiasm (or, in some cases, consciousness): what kind of normal man wants to have sex with someone who doesn’t want to have it with them?

If it’s not about getting your kicks from power and domination – which this kind of rapist always swears it’s not – then why not go for someone who’s actually, you know, interested? And if you genuinely can’t tell whether they are interested or not: well, maybe they’re not nearly interested enough to take the risk.