From The TV IV

McDreamy: A very good looking and charming surgeon, Dr. Derek Shepherd
Usage: A nickname was given to Derek by Cristina in S1E2 - The First Cut is the Deepest and the label has stuck like glue, ever since.

McBaby: The offspring of Derek
Usage: What Cristina calls Meredith's suspected pregnancy in S3E4 - What I Am.

McBastard: A particularly unsavory male reference to Derek
Usage: What Izzie calls Derek in S2E1 - Raindrops Keep Falling On My Head after she finds out from George and Cristina that he is, in fact, married.

McSteamy: Another charming and good looking plastic surgeon, Dr. Mark Sloan. Formerly Derek's best friend, they parted company when Derek discovered Mark had been having an affair with his wife, Addison.