IP what´s up did an analysis on using lyrics in tweets. They found a tweet containing a complete verse of a Queen song, and asked if that’s a copyright infringement.
In his analysis IPWU concludes that using lyrics in a tweet is of course displaying part of the copyrighted work and may even be close to being a substantial part. The substantial part discussion makes the decision of whether it’s a fair use a bit harder. IPWU ends up concluding that the tweet falls under fair use. The Danisk Copyright law does not have a fair use clause, but have a rule regulating quotes in § 22. In Denmark my guess is that a tweet containing a part of a song’s lyrics will fall under the quote clause if the quote is not extensive. One problem could be the authors right to be named in connection with the quote. So besides quoting the lyrics you have to tell that queen made the song – this might be done as a link.