1492. Muggleborn Ravenclaws bringing copies of the Hobbit to school and reading the riddle scene out loud in the common room, sparking a several month long string of riddle competitions between students trying to prove they are better at solving riddles than Bilbo. Some of the older students even attempt to charm a ring that will make the wearer invisible.
405. A couple of muggleborns know a pureblood fox animagus and continuously follow them around asking “What does the fox say?”. The pureblood does not get it and makes an actual fox noise at them, but the muggleborns just shake their heads and go “hattie hattie hattie ho!” and the pureblood is just confused.