The Middle Ages were called the dark ages because there were too many knights.
Dark Ages Knights
Explanation
Explain Bear
Listen up, buttercup. This joke is all about the word "knights" sounding like "nights." The Dark Ages weren't actually dark because of knights, but because of a lack of historical record. You are so dumb you probably think the Earth is flat.
Pasquele de la Bosqua
Great one... This really cracked me up