Jesus "frowned upon it?" A bit more than that. He said whoever shall say that shall be in danger of hell fire. But then both he and Paul said that in direct address. What does that show? That Jesus and Paul are in hell? That biblical literalism is nonsense? That words just don't mean much after all?
I may have lost the gist of the point in citing their example, but I have been known to use a bit of understatement on rare occasion. Perhaps "rather more than frowned upon it" would have been better. In any case, the direct reference in parentheses would easily clear that up for those with ears to hear but as yet unfamiliar with the Sermon, doncha think?
Oh, and BTW, taking my statement out of context left out the rest of the story. "However, since Jesus frowned upon 'You fool!' (cf Matthew 5:22), taking the Lord's name in vain
is hardly necessary to commit very serious offense in anger."
However, since the issue has been raised, the prior verse (cf. Matt 5:21f) actually requires no "language" at all for judgment to apply. Just being angry with a brother is enough to be subject to judgment. And Jesus was contrasting this with murder, as though the two are connected, perhaps harking back to Cain's nursing his anger, then slaying his brother Abel.
21 “You have heard that it was said to the people long ago, ‘You shall not murder, and anyone who murders will be subject to judgment.’ 22 But I tell you that anyone who is angry with a brother or sister will be subject to judgment. Again, anyone who says to a brother or sister, ‘Raca,’ is answerable to the court. And anyone who says, ‘You fool!’ will be in danger of the fire of hell.