Prepare the shot glasses by cutting a lime in half and rubbing it around the rim of each shot glass to moisten. On a small plate add a 1:1 mixture of Tajin spice and Sugar. Dip the top of the shot glasses in the mixture.
In a cocktail shaker, add the ingredients for the shots and some ice. Shake well for 10-15 seconds.
Serve by straining the liquid without the ice into the prepared shot glasses.