It's Anti-Bullying Week in U.K. schools from 15 to 19 November. The theme is kindness, how saying one kind word can potentially break the cycle of bullying. It lends itself well to a language activity on expressing kindness.
There are lots of teaching tools on the Anti-Bullying Alliance site. The secondary school lesson plan is particularly good, with thoughtful activities about being kind, and some useful situations that could be used for brainstorming. (Scroll down to the bottom of the page for the downloads.)
This short video is a clear introduction.
Pupils should identify with this one, featuring lots of British school kids, in and out of uniform.
And if you need a definition of bullying, you can't get much more succinct than this.
The week features a nice, simple and effective awareness-raising campaign: Odd Socks Day. Pupils and teachers (or people in other workplaces) simply come in wearing two odd (different) socks. It doesn't require making or buying anything but the idea is that it can be a conversation starter. Why not ask your pupils to wear odd socks on the day you plan this lesson?