User visits Community on a site. A counter is incremented every time the page the user visits is not a Thread page type. The counter stops when the user visits a Thread page type (incrementing the counter for that page) for the first time.
It sounds like that would be a good candidate for custom events where you want to count something in a specific situation. You could set something like s.events=event52 (and event 52 will start counting everytime it is set so you would set it only on the community pages you wish.
Another potential solution would be to set something like an evar to the page type or something. So you could set it to something like s.eVar6='community page' and you could set it to like s.eVar6='thread' or other values. From there you could run the evar6 report and look at the evar6 instances metric which will tell you how many of each value happened. It would be an alternative to an event.