This is bizarre and Kafka-esque.  The male is precluded at law from claiming self-induced drunkenness as a defence but the female IS permitted to claim self-induced drunkenness as a presumption that she must not have consented, even though she can't actually remember is she did consent or not.

What I'm trying to say is that it is entirely possible that the female did consent, although she now claims not to remember and to deny that she ever would have consented, and/or that the drunken male perceived or misperceived consent as having been given.

If they were both drunk and there were no witnesses, no one can say reliably whether what happened was consensual (or perceived at the time to be consensual) or not, ergo no criminal prosecution.