BLACK EYE: something that diminishes the reputation of a person or organization. (Literally, a black eye is the dark swelling that occurs when you get hit in the eye.) Calgary Herald (Alberta, Canada), in a story about rowdy behavior by hockey fans: <<

Lakritz: Fans' behaviour a black eye for Calgary

... A better description of the Red Mile behaviour would be the British term “yob culture,” which aptly speaks to a definite substratum of rowdy, obnoxious low-lifes, male or female. What’s happening on the Red Mile is an embarrassment to all Calgarians. And it’s certainly a black eye for our city when its female residents are afraid to go to a public place to join the celebration. The Flames are their team, too.>>