You want something that will write to a file or any kind of storage when someone enters "failfish &" ($2 being a user on a channel) and then compare all values within that storage and display the top 5.
There is a script that people used to post around a lot a while ago called "!top 10", you can find it on the forums and possibly make your own out of it. I personally haven't ever tried using /filter which it does, so I can't help you there.
