Andrew Jackson's future as a badass started at the tender age of 13 during the Revolutionary War. He joined the Continental Army as a courier and was taken prisoner along with his brother Robert in April 1781.
When a British officer ordered him to spit shine his boots during captivity, Jackson refused. Not amused by the boy's defiance, the redcoat drew his sword and slashed Jackson's left hand and head, which left him with a permanent scar. The brothers were released from captivity after two weeks as part of a prisoner exchange, but Robert died within days due to an illness contracted during detention. Another one of Jackson's brothers and his mother died before the war ended, leaving him with a lifelong hatred toward the Brits.
Jackson earned the nickname "Old Hickory" because he used to carry a hickory cane, which doubled as a weapon. He dished out his most famous cane beating to Richard Lawrence, who attempted to assassinate him while Jackson was serving as President. Lawrence approached Jackson with two pistols —plan A and plan B—both of which misfired. After noticing he was out of danger, Jackson proceeded to beat Lawrence to a bloody pulp.
Jackson was known for being a serial duelist; historians estimate "Old Hickory" participate in anywhere between 13 and 100 duels. (That is too many duels by any standard.) Jackson fought his most famous duel in 1806 against Charles Dickinson, who was an excellent shot. Despite knowing about Dickinson's pistol prowess, Jackson insisted that he fire first. This American Heroes Channel video illustrates the events leading to the duel and why he gets our vote for 'most badass American president.'
American Heroes Channel, YouTube