Business Insider interviewed Chris Scott, who came up with a funny tweet that was re-Tweeted thousands of times, often without attribution.
People changed the wording slightly and then sent it out as their own.
One comedian even accused him of stealing the joke, claiming he'd said it on TV. When challenged to be specific about when he'd said it, he withdrew the accusation and apologized.
What I find most interesting is Scott's interpretation of the phenomenon:
"It's a genuinely fascinating and foreign concept to me, to see something that you connect with on some level and then decide, 'Well, that's mine now.' My hunch is there's a sizable chunk of people who don't really grasp what plagiarism is or why it's wrong, and they kind of regard Twitter and social media as this giant free-for-all where everybody's just constantly taking and posting whatever they want from whoever they want."
One could argue that since people are not benefitting financially from their Tweets (nor are those who are plagiarising them), this is not such a big deal. What is a big deal, though, is that this attitude spreads easily to appropriating content in general, including going to pirate sites to download material that is essential to the financial survival of the people who created it.
I don't know whether this attitude can be reversed, but writers and other creators will need to find a way to deal with it. Many musicians have turned to live performance as their primary source of income, but I don't think too many people will pay us to read our novels to them.