Dave's seen the writing on the wall. He's been kicked out of many places before (including this one, it seems), and knows the drill- delete everything, and attempt to drag anyone else down within his reach on the way out.
That is the trouble in allowing people like Dave an extended stay. Showing them kindness just leads to further turmoil. They bring bile and venom with them everywhere they go- there is nothing good that ever comes of it except the final parting of the ways.