Basically, it comes from a speech she gave in May 2023 at a White House event about Hispanic excellence. In her speech, she also touched on how the democratic party can better support young leaders by understanding the context they grew up in.
This led into her personal anecdote from her mother, saying:
“My mother, she would give us a hard time sometimes, and she would say to us ‘I don’t know what’s wrong with you young people. You think you just fell out of a coconut tree?! (Laughs) You in exist in the context of all in which you live and what came before you.’”
This basically took off and got mixed up with the whole “pill meme” terminology. Those that wanted Biden to pass the torch to Kamala started saying they were “coconut-pilled” and the rest is history.