“Colossal” has such an easygoing, offhand vibe, and takes such pleasure in its characters’ foibles, that it camouflages its deep subject, which is rage. Gloria and Oscar only look like slackers. They are twinned — and also opposed — volcanoes of frustration and resentment. The disproportion between their personal feelings and the wanton destruction of real estate and innocent life is both comical and horrific, and also oddly persuasive. Inside each of us is a colossus with the power to smash everything to pieces.