You searched for: “pygoscopophobia
pygoscopophobia (s) (noun), pygoscopophobias (pl)
An "internal writhing" or pathological hatred that someone is watching the subject's behind or one's rump: Becky had a very good figure, but, suffering from pygoscopophobia, certainly had an intense dislike of men looking at her bottom, so she tried to wear very simple and dark clothes.