Do you know how serious "chopsticks upright in rice" is? I had a Chinese teacher who mentioned the taboo (with regard to China, not Japan), but she also said that while people recognize that it's something you're not supposed to do, it's not taken seriously either.

I do. My parents (americans) lived between HK and Taiwan for a decade before I was born, and growing up, I was fortunate enough to have my folks teach me a bit of chinese. We'd regularly go to a local Chinese restaurant where the staff would speak to me in Chinese so I could practice speaking. Seeing as some of the staff were significantly older, my dad taught me to be hyper aware of customs surrounding dining norms and etiquette. One day I accidentally left my chopsticks in the rice bowl while there was still rice in it, and the waitress (an older Chinese lady) saw it - poor lady nearly fainted.

I did not make that mistake ever again.

For context - it's a way of saying "death to your family" or something akin to that.