An internet style response for a period of
interactive amusement followed by an abrupt realization that you are no longer amused. Legend has it that
Queen Victoria uttered the phrase right before her much more famous phrase, "We are not amused."
It could mean that you were laughing along with a joke and didn't get it, or when you finally did get it, you didn't like it because you realized that you were the butt of the joke, or it could be when you have just realized that
the speaker was not joking.