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.
From Redditor /u/startin2stack:
Wearing saran-wrap around my arms/legs to avoid creams/lotions from rubbing off when I went to school.
From Redditor /u/KingBooScaresYou:
I'd always go downstairs on Christmas morning after opening all my presents in my parents bedroom, and there would be an unflushed sh*t in the toilet, and every year my mum would be outraged that Santa didn't flush it. Even used fake snow on boots to make it look like he walked in and sat down...
From Redditor /u/Charliegirl03:
My dad tried to 'kill' the Easter bunny every year. He would literally run out into the yard with his gun and take a few shots. Then he would come back inside grumbling about how he would get him next year.
We thought it was both terrifying and hilarious. I didn't realize how weird it was until I told people about that tradition later in life.
From Redditor /u/jamie9999999991:
Wash our *sses with a bowl of water after taking a sh*t. My family is from India/Sri Lanka so they never really used toilet paper over there. When I was young I thought the roll of toilet paper by the toilet was just to blow your nose while taking a dump.