Jason Derulo Goes to Rehab ... Addicted to Ass

Jason Derulo checked into Rehab this weekend -- the legendary Las Vegas pool party at the Hard Rock -- where the singer had to follow a 12-step program of his own:

Step 1 -- Admit you are powerless over ass.
Step 2 -- Embrace and enjoy.
Steps 3 through 12 -- repeat Step 2.

Get jazzy on that.