We've covered the topic of using your wireless router's SSID name to just plain harass your neighbors, and we've even suggested using it to discourage neighbours from leeching your Wi-Fi and rounded up some clever names for doing that, but what if you don't want to be a jerk for no reason?
In addition to changing your Wi-Fi to something scary such as "IllegalActivity" or "ISeeWhatYouAreDoing" in order to scare off people from leeching onto your network, you can also use it to send a message. "Apt112IHaveYourMail" can tell people to come to you to get their mis-delivered mail (though why you wouldn't just put it into their mailbox is beyond me). "TurnDownYourMusicPlease" is useful for considerate neighbours that don't know their sound is bleeding into your space—but not useful for those who don't care.
You could also turn your Wi-Fi network name into a challenge question that your friends would know the answer to, the answer to which would act as your password. For example, "NameOfMyFirstPet", "AdamsHighSchoolMascot", and so on, and save yourself the trouble of having to deliver your password to everyone on the planet. (They clearly wouldn't be the most secure passwords on the planet.)
Other messages like "PartyNextFriday303PleaseAttend" is cooler (though maybe less effective) than going door to door and slipping a printout in the crack, and "LostDogCall2125551234" is pretty self-explanatory.
If you're really intent on causing problems for jerky neighbours, options like "DogAbuseIn411" can deliver your messages of harassment with very little effort.
Probably the most evil thing you could try: Change your SSID to the name to the name of your neighbour's Wi-Fi. If you could manage to program your DD-WRT router to log incorrect login attempts (this script and this page on brute force attacks are the closest we could find), you could in theory capture your neighbor's Wi-Fi password, then subsequently leech off their internet.
Of course, we trust you wouldn't do that anyway. Got a clever SSID usage of your own? Let's hear it in the comments.
Lifehacker's Evil Week is all about topics such as password cracking, social hacking and other questionable tricks to make sure you're in the know. Knowledge is power, and whether you use that power for good or evil is in your hands.