You're almost certainly not actually the first poster in the thread in which you are posting 'first'. The first poster of a thread is, by definition, the OP. Yes, you might be the first person to reply to any given thread, which may tempt you to post 'first'. Indeed, when someone posts a thread, the forum will show that there are zero replies until someone replies for the first time. However, if you look at the post number on the top right corner of your post after posting 'first' and engaging in a self-aggrandising pat on the back, it will almost invariably not be #1. There is one exception to this, which is where you are an OP who has decided to post a thread devoid of any content save for 'first' for whatever reason. In all other scenarios, your 'first' means nothing. If you posted 'second', that would make more sense, because your post would be the second in the thread. But you are not, and never will be, 'first' if you are replying to a thread wherein a first post (the OP) has already been published.