Here are my ideas:
(A)Not showing someone their karma score ever, unless it is negative.
(B)Leaving a line between the comment field and the reply button saying, "Stay constructive."
(C)That line of text could link to the guidelines.
(D)Detect if someone says 'idiot' and then change the line to, "You said 'idiot', do you still want to post?"
I like this idea. In particular, I like the idea of analyzing content - but not programatically rejecting the post completely. Another forum that I frequent tries to keep things civil by banning certain words. Sounds good on paper, but then you try to use the phrase "knee-jerk reaction" and the system rejects your post because it has "jerk" in it. D'oh.
Pointing out the possible (but not definite) incivility, but allowing the post anyway (after a confirmation step) could be a nice way to remind people to be polite, but without being overly draconian.