The Chesapeake Affair, which is also sometimes called the Chesapeake-Leopard Affair, took place in 1807. This was an incident in which a British warship, the Leopard, captured an American warship, the Chesapeake, after a very short battle. This humiliated Americans and enraged them. It helped to bring about the War of 1812.
After the United States gained its independence, the British acted in ways that were deeply insulting to the United States. The most relevant way in which they did this (for this question) was by impressing sailors off American ships. That means that they would stop US ships on the high seas and remove sailors from them, forcing them to join the Royal Navy. The British commonly impressed sailors from British ships and seaports into the Navy, so impressing them from American ships was, in essence, the same as saying that American ships were British ships. It was also rubbing the US’s face in the fact that it was weaker than Britain.
The Chesapeake Affair happened when the Leopard fired on the Chesapeake in order to force the Chesapeake to stop and allow the British to search the ship for alleged deserters from the Royal Navy. These alleged deserters were found and impressed. The fact that Britain had done this to an American naval ship, which was unable to defend itself effectively, outraged and humiliated Americans.