The main requirement is that the potential date has some qualities that the father hates in people, and this motivates the daughter to love her date more.
The two got very drunk and hooked up for one night and he lost his virginity to her. It was quite a shock when he met her again his junior year and she turned out to be his new sister-in-law.
Brooke finds out him and Peyton have broken up, and they decide to hook up.
As they go upstairs and undress, Nathan gets a video camera out and they make a sex tape.
Although reluctant at first, Brooke is persuaded by Nathan who promises no one will ever see it.
The following morning, the two decide to keep it a secret when Peyton and Nathan get back together again.
In other cases, he might see something of how he himself used to be, be it pluckiness or some immature behavior, in the boy and be worried that he will make the same mistakes.