Originally create and used as a form of sarcasm, but nowadays used by thrill seekers and extremists to describe extremelydifficult maneuvers performed perfectly.
"That 720 was Awestum."
"He did an Awestum shred of that wave."
"Her Tits are Awestum."
"He smash the pipeline. He's Awestum."
Awesome and bum (The English definition; abbreviation of buttox) combined, though contrasting as 'bum' would normally imply negatitivty, e.g bummer, and awesome being that of positivity. Because of this conflict in definition, is sometimes used sarcastically. A catchy oxymoron that's funner to say that awesome.