Everyone grows up differently, which means each person learns a ton of weird behaviors that aren't normal outside of their family. Since most parents already developed quirks of their own, it makes sense that their kids normalize weird behavior as they grow up. As awkward family photos also reveal, plenty of children grow up around strange behavior that their families normalized; sometimes it's for the better, but usually it's for the worse. After all, some of the more outrageous behaviors people thought were normal growing up veer into some questionable practices that should have stopped years ago.
As for where it comes from, much of this normalized strange behavior merely stems from dad humor, the birthplace of all your deep-seated insecurities. Others simply come from cultural misunderstandings or misconceptions, which are unfortunately left to the children to figure out for themselves. Plenty of Redditors experienced their own normalized idiosyncrasies, showing that tons of people grew up just like you. Well, sort of; nobody but you eats pasta like that.