Almost everyone coins or uses expressions that make sense to only a few people. What word or phrase do you use most often that you have to explain the meaning of to others?
The one I'm the proudest of is from the early 90s, and this was used before Joss Whedon used it. I'm proud of it because almost all of my circle of friends started using it instantly:
"He's a good guy, but his Kung Fu is poor..."