Banksy

how does it not have a function?
many of his works are monuments or memorials (see monument for v tatlin), which (i think obviously) serve a function in society.
also his work serves to (attempt) to alter ones understanding of the gallery space, and to (hopefully) make one reconsider ones role as a spectator both within his own work and in art in general.
it also made him a hell of a lot of money. and a name as an art critic

It has no function other than to exist i.e Art. An object is, well, objective within purpose.

If an object provokes a thought or an action that's not a function; merely an interpretation by a subjective individual.