Hell's Angels '69

Two rich brothers want to rob a Las Vegas casino, just for the fun and thrill. They decide to use the Oakland Hells Angels as dupes in their plans by pretending to be members of an East Coast motorcycle club/gang and winning the Angels' trust, and then using them to create a disturbance outside the casino while they are inside robbing it. Everything goes as planned—the brothers even manipulate the Angels into telling them to go away—but then a small mistake results in the Angels figuring out that they've been used—and nobody makes fools of the Hells Angels.

It turns out the two brothers are step-brothers, and that only one of them inherited money. The other lives off his brother's generosity and doesn't like being beholden. Rich brother planned all along to return the money once they made their get-away and "got away with" the robbery. Poor brother thought they were doing it for real and that half of the take would be his to keep.

The movie is noteworthy is having prominent members of the Hells Angels play themselves. 

Two brothers have a plan on how to rob the Ceasar's Palace in Las Vegas. They join a motorcycle gang and while the others are drinking and partying outside of town, they change their clothes and head off to rob the casino. Of course, the police do not look for two well dressed criminals among the Hell's Angels.