I once had a coworker who drove me a little nuts. She was technically my superior, but was dumb as rocks. I went to pick up a pizza for us once and ate a slice on the way back. When she realized it was missing, I told her they forgot to make that slice. She believed me. Another time, I helped her air up one of the tires on her car. I told her she was really lucky because it only went flat on the bottom. She was elated over the good news.
A lot of that was just my normal silliness, which anyone with an ounce of intelligence would catch and either play along or call me on my bluff, but this girl never did. The times I did try to explain to her that I was joking, she got even more confused, so I quit bothering to straighten out the misunderstandings and just let her believe the outrageous things I'd tell her.
I swore to myself for the longest time I would leave my mark on humanity, sort of a legacy. Now I realize I'm just another blended-in grain of sand awaiting nuking into glass.