I like what ColinsMum said about figuring out where he was coming from. Could just be sick and tired of the whole darn scene but didn't make a good choice as to how to communicate that.
I'd make him do a written apology and rewrite it properly, then deal with the issue that made him do it and try to work on him developing different ways to express this (this is based on him being able to distinguish, which I don't know about him).
When my sister was that age she was like that (though we didn't use the word "sucked", and its very, very common now) someone said to her "you can catch more flies with honey than vinegar!" and she scornfully replied "And why would I want to catch flies?"
Now of course she's the queen of the scout troop/mommy group/religious ed etc. and can schmooze and navigate with the best of them...she learned as she went along and matured.
