Meaning: To have the balls to do something completely insane (and way past anything seen before).
Way past dangerous, stupid, legendary, awesome, cool and/or idiotic
(This is most likely something that someone else would never consider or even dream of doing).
Context: To be a Baumgartner
Tim: John is a bit of a Baumgartner when it comes to climbing.
Matt: Yeah! I wouldn't climb that vertical cliff even if I was paid, he's got some balls.
Ben: Billy is too much of a Baumgartner on a bike for my liking.
Phil: Yeah, his BMX stunts are too dangerous.