Pay a hooker and pimp to show up at the crawfish boil insisting he did some seriously raunchy stuff to her and tried not to pay. Let the pimp get physical with him. Tell them to say he has been doing it for months, and make sure to cause a huge scene at the crawfish boil. Tell them never to break character and eventually leave.
His wife will leave him and take all of his stuff, his kids will disown him. In like 3 or 4 years when he doesn't have a family anymore and is penniless, then tell him it was just a joke. He will be mad at first, but eventually you will all have a good laugh and he'll admit you got him good. Pranks are fun.