Green’s Dictionary of Slang

ass-busting adj.

[bust someone’s ass under bust v.1 ]
(US)

1. exhausting, tiring.

[US]R. Roth Sand in the Wind 42: And we had these ass-busting working parties every fucking day.
[US]J. Hurling Boomers 31: A day of heads-down, ass-busting work.
[US]Cincinnati Enquirer [Internet] It is ass busting work. I routinely take breaks and pretend to take notes so I can rest.
[US]Salon.com 4 May [Internet] The crushing economic realities and the graceless development of the American West are forever encroaching, making work as a modern-day cowboy a monotonous, ass-busting job.

2. remarkable, amazing.

USA Today.com 15 Feb. [Internet] Have you ever thought of coming to Moscow and St. Petersburg, Russia and putting an ass busting performance in front of Russian audience?