Take somebody’s name in vain
Definition 1 of 2
Pro Tip 1/3Religious Sensitivity
Using the phrase in religious contexts might offend believers if misused. 
Be mindful when you say 'Oh my God,' as it could take God's name in vain.
Pro Tip 2/3Cultural Interpretation
Different cultures interpret this phrase with varying degrees of seriousness. 
In some societies, taking God's name in vain might cause serious social repercussions.
Pro Tip 3/3Historical Usage
Historically, this phrase referred to breaking an oath made under God's name. 
They accused him of breaking his promise, effectively taking God's name in vain.