Time Paradox of the Ladder

You are standing on the top of the ladder, looking down at your past.

As you gaze into the abyss of yesterday, you ponder the question:

If a man with a moustache and a penchant for existential dread walks into a bar, and he orders a beer, but then he doesn't actually exist in the past because he's from the future... do you serve him the beer or the paradox ensues?