Disable the use of "pre" tags or enforce maximum line lengths for "pre" sections on comment threads. Long "pre" lines widen the entire page width so you have to keep scrolling right and left to read. In addition to accidental problems, you might also run into problems with trolls.
http://news.ycombinator.com/item?id=280852
The other post gives a nice example of where the problem actually occurs. Note that contrary to what the other item says, the issue isn't actually "code" tags per se, but "pre" tags.