Why are we pretending like Lulu isn't high?
"Yup, that tasted purple."
"You'll see more with your eyes closed."
"Nosey dewdrop... "
"Never look a tulip in the eye..."
"That squirrel looks familiar."
For years, people have been pretending like she's this child-like character but according to her lore, she is centuries old. We have been accepting the notion that she just has a really big imagination but there is no way someone's personality stays the same for so long.
Conclusion: Teemo gave Lulu some really strong shrooms.