Ability to block a follower

As time goes by, the number of followers that we'll want to block will increase. Even in the last couple of days I've noticed an increase in follows from users that are obviously just following as many random people as possible - not only do I not want to follow them back, but I don't want to end up with spam from them when they inevitably set up bots to look for key phrases in my updates and auto-reply (or whatever exciting surprises they have planned...)

The ability to block a follower by adding the word 'block' to either subject or body of reply email would be useful.