Can’t exactly say it’s a father-in-law joke, but it’s the best I found when I did a quick search for them. Note: a lot of what’s called father-in-law jokes on some sites are really much more about the son-in-law (to be). Much like this one.
A young woman brings home her fiance to meet her parents.
After dinner, her mother tells her father to find out more about the young man.
The father invites the fiancee to his study for a drink.
"So what are your plans?" the father asks.
"I am a bible scholar" the young man replies.
"A bible scholar, huh", the father says. "Admirable, but what will you do to provide a nice home for my daughter to live in, as she is used to having?"
The young man replies, "I will study and God will provide for us".
"And how will you buy her a beautiful engagement ring, which she deserves?" asks the father.
"I will concentrate on my studies and God provide for us", replies the young man.
The conversation proceeds in this manner, which each question the father asks, the young man replies that God will provide.
Later, the mother asks, "How did the conversation go?".
The father answers, "He has no job and no plans, but the good news is that he thinks I am God".
Also, at least Brian isn’t denying where he got his, um, inspiration from.