fake toe

The act of purposefully fueling and maintaining someone else's misconception over an extended period of time, often involving telling all but one person the truth of a situation.

"When I was young I hurt my toe and my little brother thought my dad replaced it with a fake toe. We never told him that it never really happened so he believes it to this day and loves to tell the story, it's hilarious - quick, here he comes, ask him about it!"