The Ammonite king does and his son succeeds him. David send a group of men to express his sympathy for the passing of his father. The kings nobles convince him that David only sent the men as spies with malicious intent... in retaliation, he shaves the men completely and cuts out the back of their robes-exposing their butts- and sends them back. What the heck? I mean I know people who have taken my kind intent and turned it into something bad, but this is one a whole other level. Back then, shaving a man's head and beard was the utmost form of humiliation. And to top it off, they had to travel back to David with their bums on display.
Realizing that they may upset David once he realizes what they've done, they assemble an army. David learns about the army--attacks, and wins.
6 Now I know that the LORD saves his anointed;
he answers him from his holy heaven
with the saving power of his right hand.
7 Some trust in chariots and some in horses,
but we trust in the name of the LORD our God.
8 They are brought to their knees and fall,
but we rise up and stand firm.