This is the phrase one uses when another party in a conversation makes a dirty joke and one doesn't get it.

It originally comes from the 9 dolphins optical illusion. (Seen on 9 Dolphins Rum Bottles)

The picture was used to test a Psychological property in children. Research found that the children could not recognize the intimate scene of the couple because they did not have the prior memory association with such a scenario. Therefore, instead of seeing the couple in an intimate pose, they saw 9 dolphins.
Jessie: "I can't believe you gave me DIET PEPSI you asshole!"

Ryan: "Oh c'mon man its not that big a deal."

Jessie: "Yes it is! I'm Phenylketonuric! I can't have that fake sugar. it gives me muscle spasms and I can't sleep! It was an awful night!"

Ryan: "Oh shit. Dude I'm sorry, I didn't realize."

Jessie: "And I had to cancel my date cuz of you!"

Ryan: "Why? Cuz of Muscle spasms? That sounds like a great way to be on a date, or at least the end of the date. Just set her on top while you buck around like an unbalanced washing machine."

Ryan & Jessie burst out laughing

Malcolm: "..."

Ryan: "Get it Malcolm? Like a washing machine!"

Malcolm: "No dude, I saw 9 dolphins. What's a washing machine have to do with you making Jessie sick?"
by Baked Wordsmith October 12, 2011
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