I like those McDonald's hacks where people exploit flaws in the price calculations to get burgers for free. IIRC in one case they noticed that you could order a

I like those McDonald's hacks where people exploit flaws in the price calculations to get burgers for free. IIRC in one case they noticed that you could order a hamburger without patty, and it had a slightly negative price. So they ordered twenty hamburgers without patty and one normal hamburger, and got all free of charge.