I've been thinking about the tricks that some of the fae are said to play on mortals; but the tricks were not only to the one side.
There was once a green hill near the village of Pennygown (Peigh'nn-a'-ghobhann, The smith's penny) said to be the home a benevolent group of Fae. People of the village wanting work to be done, such as spinning or weaving, would leave the raw materials on the hillock at night, after saying what it was they wanted done with it, and the next morning, the work would be there completed.
Well, one night, a jokester placed the wood of a fishing net buoy down and asked that it be made into a ship's mast. All night long, the Good Neighbours could be heard toiling on it, singing a song of complaint. "Diomaich is mi-bhaidh air an fhear a dh'iarr oirnn cran mòr luinge fada dheanadh de mhaide bhola." "Short life and ill-luck to he who asked us make a long ship's mast from the wood of a fishing buoy."
The next morning, the job was not done and the Fae of Pennygown never again did any work for any one.
The company of Fae living near Green Lock (Lochan Uaine) on Ben Lomond had a similar tradition, also broken by the actions of a mortal, although this was an honest mistake in communication, not the act of a self-deluded wit. Whatever was left overnight near the loch - cloth, wool, or thread, would be found the next morning dyed to whatever colour desired, provided a specimen of the colour wanted was left with the raw materials.
One night, a person left a quantity of thread at the loch. Wanting half dyed black and half dyed white, they left a piece of each, black thread and white, twisted together. The Good Folk thought that he wanted the pattern followed, and the work was to be done at one and the same dyeing. Angered by the presumption, they left all the thread undyed and never did task ever again for any mortal.
In my opinion, the jokester of the first tale and the too-efficient weaver of the second got off very easily indeed. The Fae have no sense of proportion, as we mortals judge these matters. Lore tells us that they are quite capable of striking a mortal who offends them blind, or lame, or visiting death upon their families to several generations, all in retribution of crimes that seem quite trivial to us.