A haircut is the weekly/monthly/yearly process of having the hair of one's head (exluding the face) shortened or remove by use of scissors
or razor blade
I have my mother cut my hair. Of course, I would be as happy to let my hair grow, as to shave it all off, as to selectively bore tiny shaver holes into the lot. Knowing that my mother will not do anything ridiculous gives me such security in asking for the most bizarre creations; I will not receive.
The worst haircut that I can imagine having is the Klingon hairstyle, wherein one shaves the front 8cm off of the hairline, and grows a very long lock of hair down the back.
Update: my current (May 22, 2002) haircut is the opposite of the Klingon cut, wherein I have shaved all of my head save a tuft in the front on the top. It gives me an elfish air.