Back in January, I told the story of some 4-year-olds' concern for taboo language:
A: Do you know the bad words?
B: Yes. My mom says them all the time.
C: Mine too.
A: I know the S word.
C: [covering her ears] Don't say it! Don't say it!
B: [trying to put his hands over A's mouth] That's the worst one! Don't say it, we'll get in trouble!
A: I'm going to say it! "STUPID." There, I said it.
C: No! No! You can't say that! Don't say it again!
As I failed to point out at the time, there is scriptural support for their worry, at least with respect to the closely-related F-word -- in Matthew 5:22.
21 Ye have heard that it was said by them of old time, Thou shalt not kill; and whosoever shall kill shall be in danger of the judgment:
22 but I say unto you, That whosoever is angry with his brother without a cause shall be in danger of the judgment: and whosoever shall say to his brother, Raca, shall be in danger of the council: but whosoever shall say, Thou fool, shall be in danger of hell fire. [Matthew 5:21-22, King James version]
The NASB translation is:
"But I say to you that everyone who is angry with his brother shall be guilty before the court; and whoever says to his brother, ' You good-for-nothing,' shall be guilty before the supreme court; and whoever says, 'You fool,' shall be guilty enough to go into the fiery hell.
In the original Greek of the gospel, these would have been an R-word and an M-word. Here's the version from Perseus, in transliteration (you can go to Perseus and re-set your preferences for the Greek-letter version, if you want it):
 Egô de legô humin hoti pas ho orgizomenos tôi adelphôi autou enochos estai têi krisei: hos d' an eipêi tôi adelphôi autou Rhaka, enochos estai tôi sunedriôi: hos d' an eipêi Môre, enochos estai eis tên geennan tou puros.
The two Greek insults referenced in the passage are transliterated as rhaka and môre (vocative of môros). The Liddell-Scott Greek lexicon glosses rhaka simply as "Hebr. word expressive of contempt", referencing Matt. 5.22; though I suppose that it should be Aramaic, not Hebrew... L-S glosses môros as "dull, stupid" (of people) or "insipid, flat" (of taste), which is the source of English moron, as the OED explains:
[< ancient Greek μωρόν, neuter of μωρός, [...] foolish, stupid (further etymology uncertain: a connection with Sanskrit mūra foolish, stupid, is now generally rejected). Perh. cf. earlier MORIA n.
Ancient Greek μωρόν is used as a noun in the sense ‘folly’, but is not used to denote a person (the neuter usually represents inanimate categories).]
Jesus would have been speaking Aramaic, so Môre is Matthew's representation of some Aramaic insult relating to lack of intelligence or sense, and more hurtful than Rhaka.
It's easy to read Matthew 5:22 as supporting the 4-year-old's belief that such insults are religiously forbidden behavior, but the theology here (as often) is obscure to me, since in Matthew 23:17, Jesus himself calls the scribes and pharisees môroi kai tuphloi "ye fools and blind".
Anyhow, Matthew 5.22 and its relationship to a phrase in Shakespeare's Merchant of Venice has been discussed in various weblogs recently, because of a comment by "Jennifer" in a discussion at reason on the NEA. An anecdote in an anonymous comment is even less certain to be true than an anecdote told by someone who identifies themselves, but this one is plausible:
Posted by Mark Liberman at June 12, 2004 01:12 PM
I taught "Merchant of Venice" to seniors one year; in it there's a line where one character is insulting another, by saying something along the lines of "He damns the ears of all who hear him, by calling him 'fool.'" One of the kids asked me what that meant, so I explained that one of the lesser-known verses of the Book of Matthew has Jesus saying that anyone who calls another a fool will be damned. [...] I went on to talk about the very funny use Voltaire made of that in his essay "The Jesuit Berthier" (an angel tells a priest to stop giving his stupid, boring sermons, because instead of winning souls for God he's endangering the souls of all who hear him, because they all call him a fool), and explained also that this is why cartoony villians in movies developed the habit of using "Fool!" as their default insult; for people familiar with the Bible, the fact that the villian always says "Fool!" is just one more proof that this is an evil, evil dude.
"So anyway," I said to the class, "back in Shakespeare's day, when people were far more familiar with the Bible than they are now, instead of insulting someone by saying 'You are a fool,' you'd say 'You are a--well, I can't SAY what you are because then I'd go to hell.' That's what he's doing in the play."
Next day I get called into the principal's office; some parents were FURIOUS that I had told their kids that Jesus said anyone who says 'fool,' will go to Hell.
"But he did," I pointed out.
"It doesn't matter, Jennifer. You can't insult kids' religions."
"Well, the kid asked me what that line from the play meant! What was I supposed to do?"
"Just tell him you don't know."