If you don't handle hot (NOT SPICY, the
temperature) food or drink well, and you have to let it cool before you try it.
It came from a literal
translation of the Japanese word 'Nekojita' (猫舌), which is used to describe someone who can't handle (piping) hot food or drink.
"Is there
something wrong with your soup? Do you want
something else?"
"Oh no I haven't tried it yet, I'm
letting it cool first."
"Oh, so you have a cat's tongue, got it."