1. excessive or inappropriate closeness or informality in a relationship, especially one that should maintain professional or social distance
Usage: uncountable noun; often used to describe behavior that crosses boundaries
2. the state of knowing something so well that it no longer seems interesting or special
Usage: uncountable noun

Examples

• The manager's overfamiliarity with employees made it difficult to maintain professional boundaries.
• Overfamiliarity with a song can make you tire of it quickly.
• She felt uncomfortable with his overfamiliarity on their first meeting.
• Repeated exposure led to overfamiliarity with the material, and he stopped finding it engaging.
• The coach was warned about overfamiliarity with the athletes under his supervision.
• Overfamiliarity breeds contempt, as the saying goes.