Step 1: Go to gettwitterid.com and enter your username.
Step 2: Copy your user ID from the previous website.
Step 3: Copy the following URL:
https://twitter.com/messages/compose?text=example%20text&recipient_id=1001
Step 4: Replace example%20text
with whatever you want the message to say. Remember, characters must be escaped (no spaces allowed)!
Step 5: Replace 1001
with the user ID you received from step 2.
Step 6: Tweet the URL you just devised to the world.