The Dirty Cheese Trick occurs when a person hands a coupon (painted with liquid cheese on the back) to a store clerk, and the store clerk gets nasty cheese on his/her hand.
Specifically, the dirty cheese trick is accomplished by taking a cookie coupon at the restaurant Fuddruckers, and painting the back of it with Fuddruckers' Jalapeno Cheese, and then handing the cookie coupon to the bakery attendant front side up. The unsuspecting bakery attendant will grab the coupon and get Fuddruckers Jalapeno cheese on her hand. Voila!