The moment a topic becomes trending, it gets overrun with spam and shitposts by attention-seekers who know exactly where to find attention. That's not the best first impression.
This was why I put together our trending search feature @ http://theenginuity.com on the front-page.
We compile a list of social trends from our indexes of social data and make it easy to instantly figure out what's going on based on your language / region settings.