People have found plenty of weird glitches with Siri over the years, but this is one of the most unexpected ones . . . especially since she and Apple are so against anything FILTHY.
A guy on Reddit just found that you can get Siri to drop a surprise F-BOMB with one very innocent request.
He found that if you ask Siri to define the word "mother," she'll tell you the basic dictionary definition, and then ask if you want to hear another definition. And if you say, "yes," Siri will respond that mother is, quote, "short for mother[effer]."
It looks like it's happening because Siri pulls the definition from the Oxford Dictionary, which lists that second definition as, quote, "vulgar slang."
You can try it out for yourself on your iPhone, although there's a chance Apple will patch it up.