We provide all Twitter users with the ability to block other users. Blocking prevents a user from following you, sending you an @reply or @mention, or putting your account on any of their lists.
To block a Twitter user:
Blocked users are unable to add your Twitter account to their lists, and we will not deliver any of their @replies or mentions to your mentions tab (although these Tweets may still appear in search). We do not notify a user when you block them, but because they will no longer be able to follow you, they may notice that they've been blocked. Your profile picture will not appear on the blocked user's profile page or in their timeline. Please note that if your account is public (i.e., not protected), your Tweets will still be visible on your public profile page.
If you change your mind, you can easily unblock a person by clicking Undo or unblock from the blocked user's profile page.