What was the most significant moment in the history of Barney and Patrice's relationship on How I Met Your Mother?

The relationship between Barney and Patrice on How I Met Your Mother was a tumultuous one, with many ups and downs throughout the course of the series. However, the most significant moment in their relationship came in the ninth and final season of the show.

After Barney and Robin's engagement falls apart, Barney begins to spiral out of control and resorts to his old ways of manipulating women. However, he soon realizes that he has genuine feelings for Patrice and decides to pursue a relationship with her.

The most significant moment in their relationship comes when Barney proposes to Patrice in the most elaborate way possible, involving an entire flash mob and a heartfelt speech. Despite some initial reservations, Patrice ultimately says yes, and the two become engaged.

While their relationship ultimately doesn't work out, this moment was a significant one for Barney, as it marked a turning point in his character development and showed that he was capable of true love and commitment.