Pillow Fighting isn't particularly deserving of being classified as a strange game unless you can get people to play it en-masse as in last Saturday's Global Pillow Fight Day
Created by the Urban Playground movement the idea was to hold mass pillow fighting events in as many countries as possible.
The king of strange games using bedroom soft furnishings however has got to be Mattress Jousting. The game is just like it medieval predecessor, only with mattresses. To play get two players, holding their single mattresses in front of their bodies, at either end of a corridor (this is not strictly necessary but it adds to the fun for observers as in the narrow confines of a corridor it is impossible for a strike not to be made). Players can choose to hold the mattress in a shield-like fashion or for the more daring player in a lance type way.
They then run at each other as fast as they can. The player who remains standing, or less bloodied, is declared the winner.