Joke's on you

Last week, my terrible boss told me I'd be taking on a new project.

 

He didn't ask if I had time to do it, didn't offer to take something else off my plate to give me time to do it, just said, "You'll be doing this."

 

I laughed at the time, because I knew I'd taken the buyout and that any work he shoves on me, he's going to end up doing when I leave.

 

Then I found out today that all of HIS bosses have been told that HE'S working on this project.

 

Here's the quandry: Should I take the bitchy way out and just mess up this project beyond all comprehension and let him answer for it (Why was Angry Gen Xer doing it when you were supposed to be doing it? How did this get so effed up?), or should I do it as well as I can and realize how delicious it's going to be when I leave and he realizes that he's going to have to do everything?