Refers to pulling the trigger and placing a bullet (the dot) in the middle of the crosshairs (the tee). To dot the Tee, is a dark play on words indicating the job is completed with attention to detail and usually some level of violence.
Did you talk to Frank about stepping out of line last week?

Yeah, I dotted that tee.

Grab your rifle and dot the tees
by Mr Hines February 4, 2010
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