While it is always wrong to take the Lord's Name in vain, this does not fall into the category of mortal sin. For one, God is not a name, per se, and it is also so generalized that most people aren't even conscious that they are doing it.
For a sin to be mortal you have to 1.) really will it, 2.) know it's wrong, and 3.) it must be a serious matter. The commandment is really calling us to mindfulness of God's holiness and how sacred, even His Very Name is; we should never take that too lightly.
We should make an effort to keep our language elevated and certainly only speak of God with reverence and respect.
A much more profane problem is the use of the name, Jesus Christ by many who have no regard for the sacredness of His Holy Name.
In that case, you can add . . . have mercy on us, if you hear it used in a swearing manner in your presence — maybe even saying it out loud so others, including the swearer, hear you.
It may turn heads but can also give a good witness and get people to stop and think.