Leo DiCaprio Celebrates 43 at Big Birthday Blowout!!!

Leo DiCaprio had an interesting birthday party Saturday night ... in terms of what he fellow celebs chose to get him.

Robin Thicke may have slipped a present inside The Highlight Room in L.A., but probably more meaningful was that he took the mic and sang Happy Birthday,.

Director Alejandro González Iñárritu -- whose movie "The Revenant" won Leo an Oscar -- showed up humble.