When something is just so utterly ridiculous and inconceivable, it could only have been pulled off by an incredibly drunk girl, probably with a name like Hilary or Hilda.
Me: "Damn, did you see that girl on the dance floor? How did she even pull off that move, that makes no sense?"
Friend: "Yeah dude, that was straight hildiculous, my mind is blown."
Something that is bad and ridiculous at the same time.
Neither word alone can correctly describe what you are describing, and therefore you need a combination of these two words.
James: Dude, I didn't do my homework again! This is like my 3rd time...
Jason: Wow, you are terribad. Why don't you ever do your homework? That's badiculous!
James: I have to freakin eat lunch with my teacher because I didn't do my homework! Jason, why do I fail at life?
Jason: You are badiculous. What the hell is wrong with you.