If you and your group of friends want to harass and drive someone crazy you can't just have all of you mess with the person solo. There needs to be a tie together but not one that doesn't allow deniability. This is the importance of hats.

Make sure that each of you when you subtly harass your target make sure each of you is wearing a stylish and obvious but not humorous nor team related hat. Like a trilby, or a fedora, or a straw hat. But not a NFL team hat, nor a Cheesehead hat (see GreenBay). Just make sure that every time you mess with the subject each of you has a different, distinct hat on your head to signal to the person that you are harassing that it is a group of people that were you to point out the hat thing it would sound crazy.

again deniability is important so the hats can in no way be related to each other other than being hats.

But hats, my friend, is uniform enough to show them that they are under a group.