Despite his jack-assery for the company, violating a contract is still, well, violating a contract. If what he claims is true, than there is a good chance this mouth breather could walk away with bit of money.
Assuming that they don't file a counter lawsuit. No doubt if he was doing PR work, he was under contract - and he definately violated that contract. Usually they have a clause that says, in more legal terms, "we can fire you if your an asshole to customers".
As for slander/libel - those are very difficult, in terms of international law. The burden is to prove that what they said was a lie, and how/why it was fabricated, against what information they had gathered and printed. Given the events that occured, a judge would more than likely throw these claims out.
As for him QQing about not making a living - he works in Public Relations. The point of Public Relations is to deal with unsavory attitudes or practices and to promote the companies interests and campaigns. There is more, but that's the surface. If you're dumb enough to flip shit at a handicapped person because they asked you politely when a product is shipping, you sunk your own ship. You never yell or threaten a customer. Ever.
You also don't threaten to sell their goods, threaten that you stole thousands of credit card numbers from various transactions, threaten people who set up some of the most important trade shows in the industry, who also has his own prominent media outlet - and above that, expect that business will be booming. You lost your job over your own actions, not anyone elses.