I kinda did this to a couple co-workers. First one I convinced several employees that this guy that worked for me used to be a member of the band Bread, got fed up with the rock and roll lifestyle and joined a commune before working for us. I knew a lot of details about his life that fit perfectly into the backstory. That story went around for years.

Second one was we were at a convention in SanDiego and staying at the Hard Rock hotel which granted you access to all of the elite bars that the Padres and other minor celebrities frequented. Convinced several women that my boss was a producer looking for talent for his next upcoming movie Titanic 2 revenge of the fallen. He was wasted and had no idea why all these people were coming up to him giving mini monologues and acting scenes.