Comment-related Plugin – Available or Should I Code It?

Okay, so lately I’ve been getting lame one/two-word comments on my blog. I’m sorry but ‘nice layout’ or ‘lol!’–that’re completely irrelevant to my entry–are getting annoying. So I’ve come to the conclusion that there should be a WordPress plugin that makes it so you HAVE to type more than two or three words before it allows you to post your comment. Kind of like how LiveJournal doesn’t let you post a comment if the comment field is empty.

Is there a plugin like that around, or should I code one myself?

Also, if I code one myself, does anyone have any site links/things I should read before I get started? I already know PHP.