Clickbait as defined by Wikipedia is:
A pejorative term describing web content that is aimed at generating online advertising revenue, especially at the expense of quality or accuracy, relying on sensationalist headlines or eye-catching thumbnail pictures to attract click-throughs and to encourage forwarding of the material over online social networks. Clickbait headlines typically aim to exploit the "curiosity gap", providing just enough information to make readers curious, but not enough to satisfy their curiosity without clicking through to the linked content.
Where do you draw the line between clickbait and click-worthy titles and thumbnails? tell us!!