(n.) an erection that invokes a feeling of self-hatred. It arises during an event that is naturally sexually arousing, despite it being a violation of one's moral standard.
Mitch got a total shame boner while watching the rape scene in The Girl With the Dragon Tattoo.
(n) An erection that arises at an unfortunate and inapproprate time. Often referred to when one is aroused by an unattractive or chubby member of the opposite sex for no obvious reason.
Alternate usage: the sensation of being embarrassed and proud of yourself at the same time.
Patrick found himself saddled with a shame boner while volunteering with a women's reading group at the nursing home.