This deletes all your tweets. Or it tries to, anyway.
It uses python and Selenium to drive a local Firefox browser to do the work. (No twitter API usage.)
Do I really need to tell you to back things up first? (Twitter allows you to download all your posts as an archive.)
HAVE A BACKUP.
Put your username and password in a file called "credentials.txt" looking something like this:
username: tweetyacount
password: seekrit
Then run the script.
Have fun!