I cannot remember which short Beckett play this is from -- its one of the very short one or two pagers I think -- but here is the best stage direction ever:
"Door imperceptibly ajar"
That is pure deadpan Beckett funny, but you maybe have to be very immersed in Beckett, as I was, when I read it. I suppose, to be fair, it communicates something to the actor about the scene, maybe. But how on earth is a set designer supposed to accomplish this? How do you take into account, on the stage, something that, by definition, no one can notice? "Door imperceptibly ajar" translates onto the practical stage as "closed." You have to love Beckett.
Not as good, but still pretty great, is the infamous stage direction in Shakespeare's A Winter's Tale. Shakespeare of course did not write his own stage directions, but you have to admire whoever got to add the equally deadpan funny "Exit, pursued by a bear" to the Shakespeare canon.