Ok, it's not an official rule but let's make it one. So, if you are registered for 1 year or more (with a minimum of 100 posts!), you can PM me with a custom title.
If you want to change it you have to wait another year so think about it wisely.
Getting a custom title with a certain amount is not a good idea imo. Rather someone who is loyal instead of someone who just posts a lot.