This is a combination of fantastic and autistic. This is a person that is autistic and has a talent that people think is fantastic. Kinda like rain man who could do mathmatical equations instantly.
It is fantastistic how he can stack those playing cards 6 feet high without having them collapse!
It can be fantastistic to be autistic when you have a fascinating ability to do something far better than almost anyone else.
Harold: I saw Sin City!
Me: That's Fanzastilistic!
Harold: I won the lottery!
Me: Fanzastillistic!
Harold: (Groaning sounds, clutches Lower abdominal area) Uhh, Some girl just kicked me in the balls and stole my money, I also found out: I'm, I'm, FILIPINO!! Dun, Dun, DUn!!
Me: HA HA!! Sucks Faggot!!!