DAK means "Deautsche Afrika Korps". It's the germanarmy in north Africa during world war II (1941 - 43). Probaly most famous man in it was Feldmarschall Erwin Rommel.
A subtle way of calling a trashy person. These are the trash of the party-- very likely the uninvited townies who crash a random party and spread their dak-ness.
Jared: Oh god, Mary-Jo and her friends showed up at the party
Sarah: Oh wow, what a dak!