Oh, it looks like there was a longer discussion about this, so I'm going to add a little more.

If you think a post is against the rules or irrelevant to your thread, use the little check box beside a post and then scroll down to the bottom of the page to click "report."

It won't get the user in trouble, and it will let mods quietly remove unrelated posts from your thread.

(Try reporting this post once you've read it to see how it works. Hope this helps!)