Image imported from derpibooru 
Original Description:
 
A splash of water hits Misty’s upper thigh where her “cutie mark” is and the supposed cutie mark smears off slightly. Which Misty wasn’t aware of at first as she saw the surprised faces of the ponies who thought she was their friend and was confused, until she felt somepony use a cloth with his mouth to wipe the cutie mark off. This makes every pony gasp and exclaim in shock. “It’s fake!”, “I knew it!”, “A blank flank?” and so on. When Misty realized what happened, she gasps in complete shock, no pony was suppose to know what she was really up to or for the fact that she was different. At least no pony knows about her spying on all of Equestria for the fire alicorn, Opaline.
 
The pony who wiped the drawn cutie mark off Misty’s upper thigh (flank) was Sideswipe.