Deja Vux is a variant of the original French Deja Vu which means "already seen".
The variant incorporates the Latin word "Redux" which means "revisited" to make Deja Vux.
It is used to describe the strange feeling you get when you're in a situation, and feel like you've been in the exact same situation before, and you know that you've already had Deja Vu about the same situation, that you are keenly aware has not yet occurred, but have already experienced.
She said, "I totally just had Deja Vux about this situation that hasn't happened yet, but that I've already deja vu about before."
He said, "Huh?"