play with loaded dice
1. Literally, to use dice that have been weighted to one side so as to increase the odds of their landing on the opposite number. When they found out we'd been playing with loaded dice, they threw us out of the club and told us to never come back.
2. By extension, to gain an advantage through the exploitation or manipulation of rules or regulations. At the height of the economic boom, investment bankers were playing with loaded dice by using sub-prime mortgages with falsified credit ratings to make as much money as possible.