There might be a way to do this, but I mean, couldn't you just stop posting and never login again if your want your account away?
Sure, we could technically do that. But we won't. We get requests to "close" or delete an account more than you'd think. 99% of the time people then come back and some even moan at us for deleting their account in the first place and not restoring it when they want it back. Whatever your reasons for wanting your account inaccessible, you are welcome to change the associated email and reset the password. Close your eyes, type some random keys and press submit. Bam, inaccessible account. If you want to be posting under a new account with good reason (being bored with your old name is not a good reason), that's fine as long as you post from only one account. You may be up for mod scrutiny if/when we notice something fishy, but you'll be fine.
Again, technically possible, but historically more trouble than it's worth for us. If you do have a good reason for wanting everything deleted, you're welcome to PM me and discuss it in private.
