A random idea today. There's a few files designed to make you feel like you're pregnant; but I was wondering if it would be possible to create a file that makes you think you might be.
For most methods of contraception, there's a chance if could be ineffective if you forget to use them. So, whatever your preference is, for a couple of days after casual sex, the file makes you believe you forgot. A little anxiety, of the kind that some people would find hot. Guess it could work for either sex.
I suppose, depending on what turns you on, the sudden realisation of your mistake could happen during sex.
For a little extra realism, you could believe that you've listened to a file that makes you forget.
I realise its a rare interest ... but who else would like to try a file like this?