No matter the reason, if you're seeking a fresh start on Twitter, this is the way to get it done.
While deleting your account and creating a new one is a viable solution, it comes with the added consequence of also making you lose all of the people you follow and your own followers. Enter TwitWipe. This is a Web-based application that will delete all of your tweets for you. Follow these easy steps to fresh and clean start for your Twitter account.
Before you start, please note: This service is a 100 percent final and does NOT back up deleted tweets in any way.
Step 1: Navigate to http://twitwipe.com on your browser of choice.
Step 2: Click the Sign in with Twitter button and enter your account information. Authorize the app on the page that loads next.
Step 3: Once authorized you'll be brought back to the front page of the site. Click the Start Wiping link to start the process.
The Web site notes that due to demand and the methods used, this process can take a little while (especially if you have tons of previous tweets on your account). It might be best to start before you go to bed or work and hopefully it will be complete by the time you come back.
If you're on a roll and want to clean out your Facebook too, check out Rob Lightner's How to delete all your Facebook posts and comments.