Usually, the point for such women is to ruin your fun and force you to have fun in the way approved of by her, in a didactic manner of course, for your improvement.

For a man behaving like that, the point is usually an attempt to assert dominance over other men the only way a weak man without humility can: hiding behind social conventions and decorum to heap abuse on others.

And Ryan is Correct, as per usual: "In the beginning was the "deed"'. After that, they're on auto-pilot the same way someone experiencing a psychotic break is.