Defacement of Facebook memorial walls

This is a recurring activity on 4chan /b/.  They find memorial pages on Facebook set up in memory of someone who passed away, and for unknown reasons post offensive comments and images on it.

Bullying of teenage girls on YouTube

This is a recurring activity on 4chan /b/. They find a video posted on YouTube by a teenage girl that, for incomprehensible reasons, they take offense to, and post a large number of harassing and obscene comments on the video page. In this case she took the video down while the offensive comments were being posted.