Usually pertaining to guys, the friends shelf is when a girl labels you a friend, disallowing you to be anything more then "just friends".
I am on the friends shelf because this girl hangs out with me and we get along great but i will never be more then a friend to her.
by Tongnar July 11, 2006
When you become an option. You are not first pick of friends. When your friend starts dating someone and you are put up on a shelf until they have no other people to hang with.
I don't need you anymore, I'm dating somebody. So I'll put you up on the shelf until I have a need for you. You are my shelf friend.
by Pix_n_stones July 15, 2017