A student recently asked how to cite to a tweet.  While the 19th edition of the Bluebook does not explicitly cover citing a tweet, it does offer some guidance in Rule 18.2.2, The Internet, Electronic Media, and Other Nonprint Resources.  Here is what we did:

We deviated from the rule in two respects.  We put the entire tweet in the title field and we added the word tweet after the URL.

Paul D. Anderson, “The Locks Law Firm just filed an 80+ player complaint v. #NFL. Now brings the total to more than 1,300 plaintiffs and 63 lawsuits.”  (April 12, 2012, 9:47 AM), http://twitter.com/#!/PaulD_Anderson/status/194799715563487232,  Tweet.

Tove Klovning and Mark Kloempken