When a lame joke backfires

I like juvenile jokes. Anything an 8th grader will laugh at will generally get a laugh from me. It was only a year ago that I asked my mom, "What are you eating under there?" She cooperated fully by stepping into the trap of a 14 year old's mind by responding "Under where?" I jumped on it immediately while laughing, "You're eating underwear?!?!" She looked at me like I was retarded.

I had a guy who worked for me named Arnold. He was from mainland China and spoke English very well. I wanted to try on one of these jokes as he really wasn't as familiar with American Junior High culture so I figured he'd appreciate some light-hearted jocularity.

I bent my index finger over and showed it to Arnold while asking the question, "Do you know what this is?"

Arnold played along and replied, "No, what is it?"

"It's buttpickers cramp...do you get it?" The idea is to illicit some recognition of the joke by getting the response "Yeah, I get it I guess." This allows you to reply with "How often?"

Arnold blew the joke up though. His reply was:

Yes, I understand. Your finger is cramped from picking your butt.

I was stunned as this joke has never backfired before. Now I was the one with buttpickers cramp and had the bent finger to prove it.

The moral of the story:

I have no idea.