Tu sors!

(une) porte = a door (the 'e' is silent)

prendre la porte = to leave (literally: to take the door)
enfoncer une porte ouverte = to state the obvious (literally: to break down an open door)
c'est la porte ouverte à... = it's an open invitation to (literally: it's an open door to...)

E.g.: c'est la porte ouverte à toutes les fenêtres! = it's an open door to all windows!

Which is an obviously absurd, meaningless but funny variation to the standard expression. It comes from the comedy La vérité si je mens (or its sequel, not sure)

It's now widely used, and I suspect some people think it actually means something :-)