Situation in which you encounter someone you know - especially someone you have not spoken to in some time - have a conversation then depart, only to immediately encounter the person again, resulting in social awkwardness.
Former neighbours A and B run into each other at the mall and chat for a while, following which:
A. It was nice to run into you!
B. It really was - send my regards to your family.
A. Take care!
Five minutes later A and B run into each other again in the parking lot and smile sheepishly at the awkward post-goodbye hello