He learned the art of bowing as British bullets whistled around his head.

From The Battle of New Orleans: Andrew Jackson and America's First Military Victory by Robert V. Remini.  Page 75.

Finally, Jackson gave the order to advance. A company of the 7th Infantry rushed forward as far as the boundary of Lacoste’s plantation and were met by brisk fire from a British outpost consisting of eighty men. In a volley that was “absolutely murderous,” the Americans drove them back to a defense line along a ditch and a fence. Additional British troops rushed to support the outpost, and their heavy fire proved very destructive.

The American artillery also advanced. Covered by the marines, it moved up the high road alongside the river and blazed away at the enemy’s outpost. It was met with such heavy return fire that the marines fell back. In a bold move, a reinforced British contingent made a rush for the artillery guns. At that moment Jackson and his staff rode by amid a shower of bullets, and when he saw what was happening Old Hickory called out, “Save the guns, my boys, at every sacrifice.” The marines rallied, and with the help of a company of the 7th Infantry they hustled the guns to safety.

It was later reported that Jackson was complimented on his ability to bow at social occasions with extraordinary grace. Supposedly he replied that he learned the art on the night of the 23rd when he bowed and ducked as British bullets whistled around his head.