I just noticed: that joke you called «inappropriate ... lousy joke for someone not in the room or having that relationship dynamic, ... a weak joke without much substance besides the shock» is actually a bathos. These suggestions of addiction, peer pressure, insecurity, doubt, urgency - they are all pathos, the mother stressed. At some point, the father intervened with a "proposal" that put all of that in proportion, and deflated the pathos into bathos. Sympathetic system, parasympathetic system. To suggest that you can laugh about it and live it healthily - also because, since you have the wits required to laugh, you can also use them to avoid pitfalls and come back home without male pregnancy and not addicted to heroin. Take seriously the things that should be taken seriously, respecting a healthy limit. As suggested by the bathos. Which "teaches" you to "breath".

I'd say there's more to it than what you saw.