I'm saying "oh MY god" ...
So, your defense is that you're not saying "oh, the real, god..." but instead "oh MY OWN god." That's no better than blasphemy. If you're admitting to having your own false god, that's breaking another of God's 10 Commandments. Read for yourself: "I am the Lord your God… You shall have no other gods before me" (See Exodus 20:2,3)
And there's even more commandments. See the 10 Commandments.
And there's even more commandments. See the 10 Commandments.