So far I haven't had that problem - but I don't think it warrants a rule on here. What people do in AIM conversations is their business, even if it involves a particular feature of a particular forum community. Yes, 2ra perhaps shouldn't be doing this - but if it upsets you, use the "Warn" feature, and then block him/her.
You should also bear in mind that his/her actions are going to make him/her unpopular in AIM conversations, and will make people think, "no, I won't read his/her story", and so, in the end, 2ra will be the one losing out. It may be annoying, but I don't think it warrants a rule, as such. Perhaps there can be an attached obligation not to do what 2ra is doing, due to the annoyance factor, but I don't think an entire new rule needs to be made and enforced.