We don't do account deletion requests, as far as I know. So if you don't want to come back, then don't. Or get a firewall and block this site.
If you don't want to get the emails for threads you've subscribed to, you can turn that off in the User CP. Should be under Options, I believe.
If you want it so that you have to log in everytime you visit, then log out, like said above, or just tell your browser not to create a cookie for this site. Should be in Tools > Internet Options.