What does Rattentaxi mean?

Around three he was suddenly gone. He took the rattentaxi again.

Dutch student slang. This is a Dutch word. You will hear it a lot at Dutch universities, student associations and in student houses.

Just leaving like that is seen as a bit rude. Unless you are too drunk to say a proper goodbye, then everyone understands. Also called a houdini. In English: an Irish goodbye. Also read what ghosting means.