Going off of what Graehm said too, its definitely not inappropriate behavior in terms of the rules. Obviously OOC conversations in the QS don't bother me in the least. RPers have no special right to make use of the Quick Sand that doesn't extend to non-RPing players. Where I begin to draw the line is on behavior that is obviously, and intentionally, spammy or harassing. Spamming means filling people's chat boxes with repetitive text, while harassing means intentionally trying to interrupt or bother people (such as persistently standing on them, animation spamming, etc).
This was definitely a case of spamming, there can be no argument about that (whether or not you want to call it RP spam is entirely your call, it doesn't mean anything to me ). Anyone who was there was well within bounds to ignore and black list if they wished. And, I'd say, since the behavior was from someone who is a member of the RP community it was not very respectful.
Such things don't really have to be done in private to be respectful, but keeping intentionally spammy stuff out of very busy public RP fora seems a reasonable expectation of basic respect for RP. To each their own, as always, but to each their own black list as well!