People say 'boo' on Halloween because it is considered as a 'spooky' time, usually pretending to scare someone.
In Hawaiian, "boo boo" could be translated as "hau'oli" which means "sore" or "injured."
Boo niey ching
boo
Boo!
because back then it ALWAYS SCARED PEOPLE!!! :)
From the scars that the Bu-Bo-Nic plague left.
Boo!
"Tengo un boo-boo." or "Tengo un dolor."
Peek a boo
Where I'm from people say "bougie". Pronounced boo-zhee.
"No me ignores boo"