A variation on the Dirty Sanchez sexual move, where the first participant eats a box of Lucky Charms 2-3 hours beforehand. This results in a more colorful and amusing feces.
Josh (on the phone): Hey girl, I was thinking we could try out the Mexican Rainbow
Josh: Awesome, let me just go to Walmart and pick up some Lucky Charms. Ben's going to be so jealous when he finds out!