First, start off but crushing your graham crackers for the rim of your cup. You can either use a food processor or place the graham crackers into a zip loc bag and crush using a rolling pin. Place your crushed graham crackers into a plate that will allow you to dip your glasses into later.
Next, use a key lime to rim your Margarita glass and squeeze the juices around the rim.
Dip your Margarita glass into the crushed graham crackers.
Second, add the ice cubes into each one of your Margarita glasses.
In a cocktail shaker or large measuring cup, add your tequila blanco, freshly squeezed key lime juice, triple sec, agave syrup, and sweetened condensed milk. Shake well or mix, if using a measuring cup, for about 1-2 minutes.
Pour your Key Lime Margarita Mixture into your Margarita glasses over the ice cubes you prepared earlier.
Serve cold and enjoy!