[gotothedoctor]

No VC would invest in this. Beyond it not being monetizable, this is a bad idea for a variety of reasons, but nonetheless, such apps do actually already exist!

These apps are pointless because, legally speaking, sex is actually not contractual (& prostitution is illegal, so no contract enforcement there either). People can, do, and are legally permitted to change their minds about what they do and do not consent to during the course of sexual activity. We may agree to sex, but we all can change our minds at any time for any reason. No matter how we felt 10 minutes ago, we are all allowed to decide actually we don't feel like it, your sheets are too gross or what one partner thought was sexy, the other thought was demeaning, or whatever--no matter what we agreed on beforehand.

TLDR: evidence of prior consent is not a trump card.