It is a mixture of the words, hilarious and bad. When something, either serious or a not so funny joke, is utterly terrible that you have no choice but to laugh at how terrible it is.
Joey: You know the show Avatar the Last Airbender?
Sean: Of course, that's like my favorite cartoon.
Joey: Yea, but the movie... That shit was hilarabad.
Slang for a type of raucous laughter in which the balls jiggle uncontrollably. Can be experienced by a woman if her breasts (i.e. female balls) also jiggle uncontrollably.
That picture of the Spotted Dick you sent me was hilarballs! My testiclesstill hurt.
Pajama casual is a term used when working from home and preparing for a video conference. All business above the waist and your pajama pants down below.