Just a thought and it's actually covered in the rules above but call this a suggestion...
If someone posts an off topic comment in a thread you don't have to freak out and point it out after the very first post. You can actually ignore it and stay on topic until the hijack grows legs and actually does "ruin" a thread.
Jumping all over the very first off topic post to scream your indignation merely accomplishes that which you seek to avoid and allows topics to devolve into fights more easily.
People who do that are no better than those who regularly hijack threads and are equally guilty of "ruining threads".
Riding shotgun on the Sox bandwagon since before there was an Internet...