I think I first learn about this and gain some conviction about this topic after I read what Douglas Jacoby wrote about this. This is the link –http://www.douglasjacoby.com/view_article.php?ID=2505
In short, what I learn from Douglas Jacoby is, I shouldn’t use those words / phrase. Reading about this topic again help me to understand why those words / phrase should be avoided.
Another author, Tony Warren, put it this way
But the fact is, saying “Oh My God” (OMG) this way, references God in vain. i.e., it is evoking God without a serious reason, reducing His value and dishonoring the title. In fact this devaluing is inherently part of the very definition of the word vain. Using the name without real purpose.
The word vain essentially means empty, or void of any real value. To take God’s name in vain is to evoke it in a hollow or meaningless way, without real significance or purpose to Him. It is essentially to treat the word God in a valueless way. So it really doesn’t take a rocket scientist to know that “Oh My God,” used in this frivolous way, isn’t really a call for God the father, it is simply used by habit or as an purposeless exclamation. Certainly it isn’t an act of Christians agreeing with, evoking, praising or petitioning God. The truth is, this phrase is almost always little more than a bad cultural or social habit.