As described in Rachael Yamagata's song "Sidedish Friend". A friend who you don't want to always hang out with you, but you want them when you call them. Someone to have as a friend only when it's good for you.
I don't want to hang out with you all the time, okay? You're not my friend, you're just a sidedish friend.
by AdamBMusic October 16, 2008