Is it considered disbelief for a husband to frequently exclaim "Oh God!" when angry over the most trivial matters, even if he says: "Why, God, is this here?" upon seeing a dish out of place?

If the phrase "lord of the thing" is uttered in a context of disparagement or dispraise, and it is intended to mean the Lord of the Worlds, then it is disbelief (kufr). However, if it is intended to mean other than Him, then it is not disbelief. The speaker is not deemed a disbeliever as long as the expression is open to interpretation, for the original state is that a Muslim remains Muslim, and he does not exit Islam except with certainty. The husband must be warned against such ambiguous expressions.