Shorena used to offer a service like that, however, it's closed down.
Theymos (or any other forum staff) most probably will not do that for you, as it takes some time they'd rather spend with more important matters.
As a result, you'd have to go through every post yourself and delete it, if that's what you want to achieve.
Randomizing your email/password and being done with it probably is the faster way here.