I’ve been playing a game on Facebook for a while now but only recently became conscious that I was playing it.
The rules work as follows:
1. Find a post on which you think you could add a clever or witty comment.
2. Read through the existing comments to the post.
3. Replace your original comment idea with one that builds on the last comment to the post.
My favorite part of this game is that more often than not, the next person to add a comment ends up playing, too.