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1.
It's heroin, but in a black, sticky, TAR like substance. It's more common and easier to get in Mexico, hence its name.
"I like Mexican Tar better than smack because it's cheaper."
by Samantha July 01, 2003
 
2.
The smell of cooking mexican tar evokes the same symptoms i expereince right before vomiting: hot, runny saliva, nausea, gagging. It is so grossly pungent & foul, but the addiction overpowers this truth & I continue.
by tabitha November 03, 2003