The first person to ever use the grammatically passive voice was joking his way out of guilt.  He got a huge laugh and from then on people not only retold the joke (” ‘The sword– went through him!‘ Ha ha ha!“) they also marveled at his avoidance of appropriate punishment (“Everyone in the mead hall was laughing their breath away! Or rather, I should say, ‘the floor of the mead hall had everyone rolling on it laughing!’ Everyone except the accused, who walked by!”).

Over time, the passive voice became less funny and less exculpatory until it is now considered a normal part of language for people who are obviously guilty or fuzzy.

The future imperfect tense also began as a joke, repeated not so much for any famed hilarity but for its perpetual usefulness.  “By the next moon, I will have begun to repay my debt in full.  And you can take that to the bank!”