The result is usually a very wet t-shirt or other item of clothing, which will be embarrassingly obvious. The sneaky wank can also be preformed lying down, and may result in come running down the leg and becoming entwined in hair. This is almost impossible to clean up, especially in a hurry. The situation is exacerbated if a friend or relative is about to walk in or actually does.
Can lead to embarrassing situations for all involved.
Person 2: Eh...no...though I would appreciate if you left the room again.
Person 1: You're sick.