As Chronos said, not something we do without good cause.
And as he also says - if you don't want to be here any more, just don't log in. If you find temptation too much, try this.
In Notepad, type a string of random characters without looking. Double click on the string to select, then hit Ctrl and C to copy. Then go into your profile, and account settings. In the "choose" and "verify" password boxes, hit Ctrl and V to paste in that nonsense string. Type your current password at the bottom, and hit the Change Profile button.
You will now have a password for the site that you cannot use, which will help you to stay away. Although password resets and reminders ARE still available, it requires a little more deliberate effort to "come back" than it does to just log in.