The legend of George Washington skipping a silver dollar across the Potomac River, an action undertaken mainly to appall Thomas Jefferson, who was mired deeply in debt at the time, was founded in accident. Washington was actually trying to kill a duck, but missed.
During his visit to Yosemite National Park in 1909, William Howard Taft's horse proved unequal to the task of bearing his 320 pounds, so the president dismounted and switched roles, carrying the exhausted steed until it recovered.
Aside from his more well-known ingenious and practical inventions such as bifocals and the lightning rod, Benjamin Franklin is responsible for the introduction of the gloryhole.
Abraham Lincoln's brief but unforgettable Gettysburg Address was wholly improvised after his dog ate the much longer speech that had been prepared for him at the last moment. He deliberately chose his famous opening words "four score and seven years ago" to then allow himself a brief pause to think of what to say next while the audience was busy mentally calculating how many years this actually was.
The long-simmering feud that ultimately led to the duel in which Aaron Burr fatally shot Alexander Hamilton had its origin in a bitter debate over whether the lager brewed by their contemporary Samuel Adams was less filling or tasted great.
Theodore Roosevelt once boxed "The Jersey Lily," Lillie Langtry, in his private White House gym. The president won by decision, though most observers agreed that he could have won outright by knockout and was merely being chivalrous by carrying the stage actress for the full 15 rounds.
John Hancock deliberately signed his name extra-large on the Declaration of Independence in a successful bid to ensure that his name would become an eponym for the word "signature". This act also had the satisfying side effect of frustrating fellow signatory Charles Cotesworth Pinckney by leaving little room for his own considerable name.
Peter Lynn is the author of the hilarious blog Man vs. Clown. He is apparently also a little unclear about who the Founding Fathers were, but he's a Canadian, so that's okay.