The person could be among people who are interested only in one another, and not the person feeling who’s lonely.
Example. Have you ever gone out with a friend and his/her old friends from out-of-town, and the group spends the entire time on “Remember When”? They talk nonstop about high school, or all the fun they had at their fraternity, or people whom they knew way back in the day—all subjects that are completely unfamiliar and uninteresting to you. You feel very excluded (and, you’re not wrong, because you can’t even join in the conversation) and just want to go home.
Example. You go out for drinks with some co-workers. You’d been looking forward to spending some time with them and getting to know them better. You’re not an office gossip, but all they want to do is trash, backstab, and talk about colleagues. You’re very uncomfortable and can’t wait to leave.