This is something I used to do more in my 20s but never knew there was a name for: the "Irish goodbye," said of someone who leaves a party without saying their farewells to the host, the other guests, etc. Also referred to, says the Slate article, as "ghosting." A young woman in our office, who married a Serbian gent and visits the country regularly, contrasts this with what she calls the "Serbian goodbye." In this instance, you have to say goodbye to everyone at the party before you can leave. She says it can take an hour and half to leave a party.