If You Make a Fool of Yourself

Once upon a time, there was a young boy at a wizarding school who, despite his formidable prowess, was exceptionally lazy and would always find the most innovative methods of shirking from his chores. Once every week, he was to animate the mops and brooms to the clean the nigh endless stretch of floors of the wizarding school's ever-winding halls, a task which he dreaded like no other. In order to avoid a day of such dreary drudgery, he concocted a plan to brew two potions, the first of which could transform a man into a donkey and the second of which could morph a donkey into a man. When the morning of his chore arrived, the boy quaffed the first of these potions to become a donkey and left the other hidden beneath his bed.
When the time came for the groundskeeper to come to the boy's room to deliver the mops and brooms, the man saw no boy, only a donkey, whom he chased out of the building. The jubilant donkey boy began to enjoy the remainder of the day in idle revelry, basking in the sun, grazing on the finely trimmed hedges, and merrily whinnying along to the songs of the birds. As his lazy day dragged on, he grew more and more naughty and began to pull pranks on his young peers: spitting into their carefully crafted potions, neighing into their ears as they sat in silent meditation, and bucking at their hissing feline familiars; it could be said that this obstinate donkey boy was essentially making an ass of himself, all the while the school's astute headmaster watched from his tower, suspecting that mischief was afoot.
As it so happened, a grizzled knight in silver armor came marching to the school with a crippled horse limping at his side, requesting an audience with the headmaster. The humble knight explained that he was on a quest to slay a mighty dragon, but he had just been ambushed by a band of kobolds on the road, and while he had escaped from the encounter unscathed, his noble steed had not been quite so fortunate and he was in dire need of a new mount for his upcoming battle. The headmaster explained that while they had no horses, they did have a rather unruly donkey on the campus that the knight may take along for his arduous journey. The knight thanked the headmaster and reined in the hapless donkey boy, who bucked in protest with all his strength, but to no avail, as the veteran knight was experienced in handling such ornery beasts. Defeated and dejected, the crestfallen donkey boy reluctantly allowed the heavily armored knight to saddle up, letting out a bewildered gasp as he bore the full weight of the knight on his back. The chortling headmaster handed the knight a familiar potion with instructions to give it to the donkey once the battle was done, and with that, he waved them off as they rode in the direction of the dragon's lair.
The moral of the story is as follows: if you make an ass of yourself, don't be surprised if somebody takes you for a ride.