Tareq's thirst grew as he trudged down the blocks to the post office. Sweat dripping from his brow, Tareq adjusted the strap of the duffle. There was a cantina nearby. The cantina wasn't air-conditioned, but they did have an attractive waitress that Tareq had seen before, and a large selection of tequila. Tareq entered the cantina and ordered a mescal, con gusano. The silvery liquor shimmered in the bottle, and the attractive waitress fished out the worm and dropped it in the drink. There was an satisfying plop as the worm hit the spirits in the glass.
Tareq eyed the drink, and then the waitress, and then the drink again. He gripped the lowball glass in his unsteady hand and slammed down the several ounces of liquor in one gulp, including the worm.
What Tareq didn't know was that the worm was an alien symbiote, and the resultant parasitic infection permanently turned him into a homosexual. While ordinarily that might have upset Tareq, the worm also robbed him of the ability to realize anything had changed. He did have to suck a lot of cocks throughout Mexico and the rest of the world, though.