Supposing I strike up a PM conversation with lots of people at once in the "Invitation" mode (it's possible, gregarious sort that I am). Some are interested and some think "WTF? I can barely remember who this person is and now my inbox pings every time she or one of her ridiculous associates [no names mentioned] cracks an idiotic pun". Can the irritated person opt out of the conversation? I haven't yet found a button for this...