Note:
'Banter' between 'friends' is treated no differently from any other forum posts. For example, if you flame a 'friend' and think that because you don't really 'mean it' then it is OK, it will still be considered as flaming and dealt with accordingly. Moderators to not have the time, nor inclination, to check with each person whether they are offended by the flaming, and it would also result in the appearance that the rules are not applied consistently.
This means that it's trolling regardless, though seeing as the idea behind it is that we don't necessarily know if something is banter or not, if we
are aware that it's just banter, we could potentially let it slide.
But then the question is, what does it look like to a lurker, or someone who isn't aware that the post is just banter? It would look inconsistent, and like favouritism. So that's a consideration that we'd have to make too.
Note that it's possible that what one participant thinks is friendly banter isn't to the other, so we'd have to throw caution to the wind and go with the rule in cases where we're not absolutely sure.
And also note that you're not talking about the usual circumstances in which this rule violation takes place (e.g. someone posts some not-so-great civ advice, and someone else accuses them of trolling, when really they were just trying to be helpful), but a possible exception to the rule.
And a final thing to note; some posters have been given specific instruction that they will not get the benefit of the doubt in interpretation, due to their history, so they should be amply aware that pushing the boundaries is a bad idea.