My partner and I were in a very casual restaurant (self seating, buffet style) with another couple who we were still getting to know. As we were about to eat, a good friend of the couple (but unknown to us) came over, and without excusing himself for interrupting or even so much as a glance in our direction, proceeded to discuss a matter in a very loud and animated manner with our new friends. Then, after about 12 -15 minutes, the person departed, again without a glance or word to us.
I was flabbergasted. It felt awkward to eat in silence (or even at all, since the other couple were not eating), and it would have been nice had the couple interrupted their conversation to introduce us, or excused themselves for "a moment" to discuss a matter totally foreign to us, but that didn't happen.
I would have considered introducing myself to the newcomer if there had been a break in the conversation, but there wasn't.
Other than that, what I was feeling (and still feel) was "How incredibly rude that guy is!"
My question: Is there any courteous way to interrupt the "intruder" and prevent being treated as if we did not exist? What is the best way to handle such an event?
I'm not looking for how to handle our new friends so much as the intruder.