Delete account by users themselves or with support from forum mods after requests sent.
It is my first time to know it.

Quote from: CryptopreneurBrainboss on November 18, 2018, 09:10:35 AM

delete this account (to avoid having multiple accounts) when account recovery is successful.

After that, I searched and found that there is no way to delete accounts. Did you miss something, fella?
Staff's answer given below.

Quote from: achow101 on April 18, 2017, 10:53:43 PM

Accounts cannot and will not be deleted. Any messages to you send to any staff member about deleting an account will be ignored. You cannot delete your account.

Another answer is here (in 2018)

Quote from: hilariousandco on March 04, 2018, 11:06:22 AM

It's not possible. Just abandon it.

Another option is send request to @Theymos, wait for his support. One more time, can not delete, just change account's name to 'Anonymous'. That's all. Nevertheless, I doubt that @Theymos has still supported this way, because it's unnecessary.

Quote from: theymos on March 08, 2012, 05:49:57 AM

As you can see here, I only change the username to "Anonymous" on request.

Based on what I got from searching time, it's impossible to delete bitcointalk forum's accounts. Abandon them is only option.