Whoever first coined the phrase "there are no stupid questions, just stupid answers" obviously hasn't been asked very, very stupid questions.
While we all have off days and different learning curves, there are some questions people ask that are so obvious and confounding they shouldn't need answering in the first place. Learning and keeping a sense of curiosity is important for everyone, and asking questions is certainly part of it, but there are indeed stupid questions.
"Is the ice cream served cold?"
Usually as a waiter, I can game-face almost anything, but there's no way my face didn't read "...the f*ck you just say?"
"Do you speak Canadian?"
I thought it was a bad joke. It wasn't.
Girl: Hey what’s the capital of the world again?
I said Detroit.
I work IT, asked a person if her mouse was wired or wireless. She said "How am I supposed to know THAT?! This is YOUR job!"