People should realize that off topic posting isn't as problematic as some make it out to be. Off-topic posts aren't really, or for that matter, shouldn't be a black or white issue in which no person should trespass. To expect a thread to act nothing like a conversation, in which the occasional digression for an example that may be loosely related to the topic is warranted at times, would be much too stifling.
I suppose part of determining which off-topic posts are kosher lies somewhere between the intention of the post, knowing the intention of the poster for doing so, and also knowing a little bit about the poster's history.
Also, the nature of each thread in a way determines the limits/degree of how much off topic people can stray. Race day threads should be pretty narrowly confined. I've never reported anyone, but the closest I've come to doing so was on a few occasions during the Giro race day threads where a small group of posters persisted in doing so despite being asked to refrain from continuing on their off-topic rambling. Clinic based threads I think allow a bit more leeway for off topic speculation because doping isn't done in isolation, in much the same way people don't learn language on their own, they learn it from others who have already done so, so speculate away.
I think if people expect a hard rule on what and when off-topic posts are forbidden they will wait a long time because it will never arrive. A little application of common sense suggests that the nature of a thread and where that thread is located should determine its limits and how flexible it is, not a strict 'no off-topic' posting rule.
That's my two cents. Apologies for the lack of brevity, if you know, that's your thing.