that's when we all three stood up
Used to describe when a situation has suddenly turned awkwardly confrontational, dangerous or tense. Derives from a scenario where three men are casually sitting down and exchanged words escalate to the point where they stand up, ready to fight or possibly reach for a gun.
...then she told me she was late and that's when we all three stood up. Come to find out she was just talking about how she missed the first 15 minutes of her psyche class the other day. Whew!