Definitions by NYBumkin

sideshoe 

Not referring to one's girlfriend, but their "other friend"....sideshoe, or mistress if you will.

When a friend sees his buddy being intimate with a girl other than his girlfriend-

Friend: "Hey, I thought you were dating (insert girlfriends name)?"
Dirt Bag: "I am dating (Girlfriends name), this is my sideshoe."

sideshoe by NYBumkin September 15, 2014