Stack Exchange seems to have made it impossible to delete accounts. I can delete the accounts from other individual sites like Ask Ubuntu, but I can't delete the main account on stackexchange.com. I want to be rid of Stack Exchange completely! I don't want a Stack Exchange account whatsoever! I really don't like Stack Exchange and I want nothing to do with it. Please help me delete my stackexchange.com account!
You'll need to contact Stack Exchange directly to request that. On a site where you still have an account, click the "contact us" link at the bottom, choose "other" for the reason, and explain that you'd like to delete your network account in addition to your accounts on individual sites. I don't know if they'll do that for you, but there's no way for you or for site moderators to do it, so asking them is your only option.
(If you reset your user name to the default "user#####" and delete your accounts on all sites, that'll be as good as gone. You won't get any notifications since those come from specific sites, so if you log out and walk away, SE will be dead to you.)