The process by which a person (male or female) is approaching the climax of an orgasm and begins to get very excited. At the actual climax they start to laugh hysterically to the point where they vomit all over themselves and then immediately follow it up by sobbing uncontrollably.
John: I had a fantabulous roller coaster last night with lindsay.
For all other human beings: fabulous, fantastic, amazing.
Specifically referring to former Washington, DC mayor, Marion Barry, "fantabulous" is the definition of a worst possible scenario. Shortly after Barry's personal publicist, LaToya Foster declared Marion Barry was feeling "fantabulous," it was revealed 57 minutes later that Barry was, in fact, DEAD.
Me: Damn man, I'm feeling fantabulous today! You: Uh, you mean like Marion Barry? Me: Aw shit, he's dead. I need to find a new word to use, huh? You: Yeah, probably. Me: The bitch set me up. Ok, I am the opposite of fantabulous! You: That's great!