The feeling of guilt when you have finished masturbating over an ugly person.
Also applying to masturbation over ugly pornographic material (e.g. fat woman).
When you are feeling seriously horny and you think it is acceptable to choose a random person to masturbate over. Either whilst looking at one of their photographs or texting/ chatting to them online. Only to realize shortly after you've exploded that they are fuck ugly, and you've just made the biggest mistake of your life. You have fallen victim to a 'guilt wank'.