If you've made a Twitter list public that should be private, you can use the "edit" function to change the setting. Click the hyperlinked name of the list you've created; in the upper left corner, you have the option to edit or delete your list, so you can change the privacy setting or nuke the thing altogether.
The great thing about private lists is that the accounts within them don't ever know. (I confirmed this using a few different Twitter accounts and private lists.) So the four career-related contacts you've confined to the "Put the keyboard DOWN and get fresh air" list will never know they're not on your Twitter A-list.
Step two: Look only at the lists important to you
Now that you've set up your lists in Twitter, forget ever going to Twitter.com to look at your stream again. Both HootSuite and TweetDeck will let you customize your application display, so take advantage of that to set up the lists you want to see, and omit the ones you don't.
Worried that someone you've put on the exile list is going to mention you in a tweet and you'll miss it, thus prompting an uncomfortable incident? Set up a column within TweetDeck for your mentions, and whenever someone retweets you or mentions you, you'll know. Although HootSuite's "mentions" tab ostensibly performs the same function, some users are reporting that this isn't working as well as it should.
Now that you've handled the Twitter irritation problem on the desktop, solve it for all your mobile Twitter browsing. UberSocial (on Blackberry, iOS, and Android) is a free app that supports all the features from Twitter.com--which means you can view or create lists. Download it and train yourself to just steer straight to your lists.
Step three: Set up another, protected account
If you're using Twitter primarily as a consumer--that is, it's become your de facto stream for news, eavesdropping on people, or looking at pictures--and you still can't drop people for social reasons, you're in luck. Nobody is really going to notice your level of nonparticipation dropping even lower, so just abandon your first account and set up a second one. Make it a protected account with a pseudonym--you can strictly control who follows you--and start following the Twitter accounts you find the most useful.
Voilà! You still have your original Twitter account for social reputation management (like avoiding awkward conversations with people when they notice you've unfollowed them), and you also have a clean, unpolluted stream of Twitter content you can sip from at your leisure.
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