A lonjunction (lazy conjunction) of the two words "stupid" and "spectacular". It essentially means stupidly-spectacular. It can have either a positive or negative connotation depending on it's use.
"Sometimes he doesn't think about what he's doing and still manages to win in a stuptacular way."
"Letting Rich borrow my car was a stuptacular idea... he just crashed it into a tree."
when you're holding up your phone and making faces at it, as though you are taking a selfie, but you're really taking a picture of the person across from you or the wall or anything else that seems interesting but you don't want to be caught dead taking a picture of.
This action is often made more convincing by wiggling the eyebrows or opening the mouth, to pretend you're trying to get a Snapchat filter to work.
FRIEND A: "Did you just take a stealthie of me?"
FRIEND B (turning phone around): "no I was just using snapchat's new filter, see?"