"Tweets are like the air. Anyone can do anything like to them, including quoting them with or without your permission. If an enterprising company wants to take something you said on Twitter and slap it on a tee shirt, they may do so. If a gent of the disturbed persuasion wants to engrave your tweet into a 600-foot swastika, he may do so."

You cannot copyright a Tweet – Jeffrey Zeldman Presents The Daily Report