I spent about 5 mins trying to find a “Delete My Account” link on Fitocracy, but came up short.
I ended up sending an email to firstname.lastname@example.org and got this response:
We’d be sorry to see you go, but we’ll mark your account for deletion whereby it drops into the deletion queue for removal within around 30 days.
The Fitocracy Team
So, just send them an email and it looks like they will take care of it for ya.
Hope this saves you some time.