It's rude to exclude others in social interactions.
John is talking to his friend at a party when Billy, an acquaintance walks up to him.
John wants to continue his conversation with his friend.
John steps back to invite Billy to listen in on what he and his friend are discussing while he continues talking.
John turns his body to ignore Billy and keeps talking to friend as if nothing happened.
Billy stands there and politely waits his turn to engage in the conversation, but he is happy to be part of the interaction.
Billy stands there awkwardly before leaving in a bad mood.