the 6-7 thing has been a source of constant amusement for me. my kid told me that one of their teachers had (with good humor) banned saying "6 7" and we immediately went down a rabbit hole of how he could "side-channel" 6 7s into conversation - like "hey, $teacher, what's the next prime number after 61?"

he told me there's a small bustling trade in learning numbers in other languages - "seis siete" for example.

seems like harmless fun to me.