You Are Dinosaur
You can tell this is an old message based on the type of meme they used. We haven’t seen rage comics in a million years. However, we gotta hand it to the letter writer: the drawing of the FFFUUUUU meme is spot-on. Bravo.
What a lovely way to make a first impression. You’re the new kid on the block, you don’t know anyone in the other apartment units, yet you’ve already managed to anger at least one of your neighbors. Judging by all the stomping around you do in your apartment, the OP could only assume that they lived downstairs to a dinosaur.