Follow this dead-simple guide to force any Twitter user—from Oprah to Kutcher—to follow you. No, seriously. (Updated)
I have no idea how a hole this large could be left in a service as popular as Twitter, nor do I understand why it hasn't been shut yet. What I do understand, though, is that Oprah is following me right now, and receiving my DMs. So anyway, here's how it works:
1. Open the Twitter web interface (I haven't been able to get it to work in the apps I've tried)
2. Tweet "accept username", as in "accept oprah"

3. Wait a few seconds. You may get a server error, but that means it's worked.
4. Check your followers list
5. !!!
This command is either a remnant of a system that isn't in use anymore, or exposes something fundamental about the way Twitter works. (Typing "follow username" lets you follow someone, too.) Either way, ha, holy shit.
source: http://gizmodo.com/5535298/how-to-force-anyone-to-follow-you-on-twitter