Most people will just edit one of their posts, just go in and change the text to 'PLEASE DELETE - DUPLICATE POST', capitals so that we notice it, and it's usually no bother to get rid of it. Don't worry about 'shouting' with the caps, your using caps to highlight the post to a moderator, there's no other way for you to do this so it shouldn't cause any problems. We might not spot your post, but at least it's something.
People tend not to care very much about duplicate posts and stuff, they are rare here because of that exact post measure, but we're far more likely to get annoyed at things like L337 speak, in fact any sort of trend like that is irritating to most of us. Deliberately bad spelling and grammar I'm referring to of course - we have people from all over the world in this forum so we are used to reading contorted English and even badly translated babelfish gibberish.