Henry Symeonis smacked Osbertus de Langetoft's balls a little too roughly one day, as a prank, whilst they crossed the Hythe Bridge from opposite directions, leaving him unable to perform any physical activity for a number of months. As Master de Langetoft was a popular student, and a sterling coxwain on the rowboat, this was seen as such a heinous crime on the part of Master Symeonis, that graduates eagerly agreed to craft a tradition of swearing an oath to never be reconciled with Henry Symeonis.

Actually, it's worse than that, but I like my version better. Nobody is murdered.