Whether someone notices that you've unfollowed him on Twitter depends on your relationship to that person, how actively he uses Twitter and whether he is following you back. Lady Gaga and Ashton Kutcher probably won't notice if you unfollow them, but your best friend probably will. While Twitter doesn't send notifications to people when they've been unfollowed, finding out who followed or unfollowed you is easy to do by looking at your follower list or by using a third-party service.

Follower and Following Lists

Twitter tracks the number of followers for every account. Your follower and following numbers are listed on your profile page. Click on the "Followers" number to see every account that follows you. If you have only a few followers and you lose one, it should be easy to determine who unfollowed you simply by looking for who is missing. This is even easier to do if you follow back each of your followers, because you can simply compare your follower and following lists to see who is now missing.

Direct Messages and Following Information

If you are following someone who uses Twitter's direct messages, or DMs, it may not take long for that person to discover you stopped following her. This is because you can only send DMs to your followers. If you sent a DM to someone following you and you stopped following back, that person won't be able to reply to you. If your former Twitter pal goes to your profile, instead of the "Follows You" notice on your profile, she will see a Follow button.

Third-Party Services

Free services like Flwrs.com, Justunfollow.com and Who.Unfollowed.Me can automatically inform people who unfollowed them and can even post this information in their Twitter timelines. To avoid public notoriety for unfollowing someone, you can check that person's profile for these kinds of bulletins beforehand. Even if someone opts not to post these unfollow bulletins on his profile, there are other, more discreet services that can show follower statistics. For example, FriendorFollow.com tells people who is following them, who isn't following back and who their mutual follows are.

Unfollowing Etiquette

Following and then unfollowing a lot of people in order to get attention is a tactic called "aggressive following," and it can get your Twitter account suspended. Other than that, there is nothing wrong with unfollowing someone who no longer interests you. To help ensure there are no hard feelings, some people opt to occasionally tweet about their reasons for unfollowing. Others even put their reasons for unfollowing in their profile descriptions, something like "I unfollow rude people." If you are unfollowing someone because she is sending you spam DMs or posting spam in your timeline, you can also choose to block the person and report her for spam when you click the "Unfollow" button.