So it's a lot like saying, "Your mind is on vacation, and your mouth is working overtime". From a song by Mose Allison.

>It is a popular expression among teens when one says something stupid, the other will reply with that phrase (I hear it when my daughter and her friends are talking)
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>>You can read an explanation below. Really, I didn't mean to offend, and it is a term (see the slang part) I generally don't use. The slang usage might be a ribbing between friends...one person might do or say something silly/stupid, then the other one might say "Did you ride the short bus this morning?"
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>>http://en.wikipedia.org/wiki/Short_bus
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>>>Must be a local thing. What's 'The Short Bus'?
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