A slang way of intonating that an object or entity fails to perform it's inteded action or purpose in a satisfactory manner.
"I say sir, your prize racehorse seems to have done a Jbad and failed spectacularily, losing you your entire fortune in rubies!"
"I certainly have pulled a Jbad today Martin my good man! Now kiss me like you kiss your most expensive whore."
What a fucking Jbad, he died on the first goomba in mario 1.