(Optional) Add salt to the rim of your serving glass by using water or a cut lime to wet the glass rim. Then, dip the rim into the dish of salt so the salt sticks on.
Add the lime juice, triple sec, agave nectar and tequila to a cocktail shaker.
Fill the shaker with ice and shake well, about 15-20 times.
Strain the drink onto fresh ice in your prepared serving glass.
Top off the drink with the beer. Give everything a gentle stir with a bar spoon just to make sure it is all mixed.
(Optional) Add the lime slice(s) as garnish, serve and enjoy!