Mugging
The state of your face makes a world of difference in how you're treated. One black eye and everyone's perception of you changes. Some people will ask you how you got your black eye, they are either brave or know you. Other people will not ask. This latter group can exhibit some interesting behavior. There will be no chit-chat in the coffee line. There will very little eye contact. There will be no "thank you"s for doors held open.
There are some benefits to the black eye, though. You will never have faster service anywhere, ever. If someone you don't know is annoying you at a bar or concert, you can deal with them with just one look. You can make children cry.
The most important lesson that I've learned from this experience is this: Don't ever tell people the real reason for your black eye. Make up a good story, something on the bitter edge of believable (in my case I told people I am a lumberjack and I had an ax-ident). A fabrication will be way cooler than the crappy way you got your black eye.