While dining at a Mexican food restaurant, a waiter sneakily convinces customers to add guacamole and/or sour cream to their order without informing them that it will add $3 (or sometimes more) to their overall bill. Can also be applicable to other situations involving trickery outside of Mexican eateries.
Waiter: "Alright, one chicken quesadilla, and would you like your guacamole and sour cream on the side?"
Unsuspecting and Distracted Customer: "Oh... sure."
Bill: "$7 Quesadilla, $3 for guacamole and sour cream on the side."
Angered Customer (who doesn't even like guacamole): "He pulled a the sneaky guacamole maneuver on me!"