Back in the days of 3.5E, I had a guy come up with a peculiar dice cheat. His character was a Fighter, and was about 15th level and all about two-weapon fighting, so he would frequently need to roll four, maybe five d20s every turn when using the Full Attack action. To save time, he asked if he could "roll all of them at once" and I allowed it.
After just three rounds of combat, I noticed he was sorting his attacks in ascending order (applying the highest attack bonus to the lowest roll, then the second-highest bonus to the second-lowest roll, etc.) so that they all averaged out. He was also applying the highest damage rolls to his critical hits, and leaving the lowest damage rolls to his misses. Thus, he rarely missed his target and always did above-average damage. I guess he thought nobody would notice?
To fix it: I made him a special set of color-coded d20s to use, "to help avoid confusion" I said.
"All you gotta do is follow the color wheel: red first, then orange, then yellow, then green, then blue. Pretty cool, huh? I even color-coded the damage dice too, so that you don't have to wonder which roll to apply critical damage to." He tried to politely decline, saying something about how he likes all his dice to match, so I suggested using the position of the dice as they landed: "read them from left to right, maybe?"
Suddenly he didn't want to roll them all at once anymore.