I've seen this happen in multiple threads whether it be my threads or somebody else.  It has happened to me and Ive seen it happen to others.

Every so often a user feels the need to start going completely off topic to talk about users and what they should or should not do(Calling them out).  I've been guilty in this as well before so im not innocent but these arguments should be dealt with in private.  There is no reason to go completely off topic just to talk about someone and tell them what they should and should not do.  That is why we have moderators.  Mods dont mod this stuff, but not only does it detract from the original topic but it is also not needed at all.

There needs to be some kind of rule about derailment as this is one of the most annoying things on VGC.

i report posts for derailment often.  Nothing ever happens either unless it also breaks another rule.

This has been my experience as well.

Edit: And there is a rule for this already:
"Keep posts on topic as much as possible. Threads do sometimes naturally transition into other discussions, but coming in and posting about a completely different topic in order to start arguments is not okay. Stay on topic, and if you have something different to talk about make your own topic."

Then  i def dont understand why there is nothing done about these type of discussions then.

I report for derailment, but usually the derailing comes with some kind of trolling/baiting, so they DO get moderated for it. The PS Nation thread was a pretty good example recently.

Though I do agree a more specific rule on the matter would be good.

YES this site needs yet ANOTHER bannable offense.

I havent been in PS nation recently so i didnt see what happened.  I guess with one of the most active threads ever on this site it was bound to happen eventually unfortunately.

You can't derail a thread all by yourself, unless you're a master troll. Like Selnor(?) said, you simply have to ignore it and continue on with the topic.

There are enough rules. >.

I often go off topic for a joke but not to try and call out users.

I see no reason why both users cant be warned if both are guilty. 

Rules has allowed this site to be somewhat ok compared to places such as IGN and Gamespot.  Otherwise you would see a lot of master trolls lol