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A sexual activity which requires the Chicago L train (preferably the blue or green line), a homeless person and enough money to pay for two ventra passes. When you acquire all of the above necessities, board the L and fuck.

There are added benefits and it's not a complete dirty l unless you end up with a tooth in your mouth that is not yours.
"Yeah, I went to Chicago over spring break last year."
"Did you do the dirty l?"
"It's not a trip to Chicago unless you do."
by lansingmichagin36 March 19, 2017
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