The diminishment of one ( or preferably anothers ) reputation and/or self esteem. Usually occurs via the insult of a second party, although self inflicted embaressment ( or indeed, both in conjunction ) can also qualify.
"Dude! You gotta take some affirmative action! Your ex is going round telling the whole party your dick is the same size as Timy's! ( the resident infant gerbil ) You're getting totally diminished out there man..."