Topic: Suggest TV Series
How about one of those threads: do something to the poster above you.
In this case - suggest a new TV series to the guy/girl that posted before you, that you think they'll like, based on their signature watchlist. [If you don't have one, create one, it's easy].
a) only suggestions for the poster before you
b) suggest no more than 3 tv shows at once
c) you can comment other people's suggestions, but you need to provide yours first, and make a clear separation between your suggestion for the person before you, and the comments to other people's suggestions.