Aforementioned means mentioned before. You use it to indicate that the person, place, thing or activity you are talking about (or, more commonly, writing about) is the same one as you were talking about earlier (or, more commonly, had written about earlier in the same screed).
For example, if you publish a blog that is a personal journal you might write a few paragraphs about your dog and then go on to bore your readers with a verbose narrative on other mundane aspects of your life. After this non-dog interlude, you might then write something to the effect of, “if the aforementioned dog does not stop peeing on the floor we are going to put it to sleep.”
The use of the word aforementioned indicates that the dog you are talking about in this paragraph is the same one you talked about earlier in your text and not some other dog.
There are a couple of points to make here. First, you should really consider not boring your readers. Boring readers is my job and I get upset when people invade my turf.
Second, I think you’re being more than a little harsh in your punishment of a dog that is, after all, only doing what comes naturally, but I sympathize with your frustration. This is one of the reasons why I can’t understand why anyone would ever want to have a pet. However, this has absolutely nothing whatsoever to do with the word aforementioned, so, never mind.