The boss gave him a ball-busting critique of his report.

ball-busting 是由 ball（睾丸）和 busting（打破、粉碎）组成的复合形容词。字面意思是"击碎睾丸的"，引申为"极其严厉的、毫不留情的"，常用来形容苛刻的批评或高强度的工作。