The person that gave them the drinks then babysits theirs, while continuing to imply the same level of drinking their encouraging the other person to.
There are entire strategies to this. Mostly it's getting a woman drunk enough to be open to something but not so drunk that they black out.
Many men don't care about the black out ... Bill Cosby, the Steubenville high schoolers.
Many men know what they're doing is wrong so they imply that they were so drunk too, hence the misleading with their own drinking while monitoring another's
Many men don't know when no means no or choose to progressively ignore nos.

That's mostly what college shit looks like. Black out drunk and passive date rape.

Hook up culture of alcohol and sex that have been going on since fermentation was invented is not the same.