By macroing the Brewmaster monk abilities Diffuse magic and Zen Meditation together, in that order, and using this macro right as/before a spell is hitting you, results in the vengeance gained from the spell being exponentially higher than if you did not use this macro.
Example:
Darkmaster Gandling Incinerate in Heroic Scholomance without using this macro gives 15k vengeance.
Darkmaster Gandling Incincerate in Heroic Scholomance with using this macro, with appropriate timing gives 113k vengeance.
The timing of the macro is essential. If you are trying to reproduce this - you will likely have to practice it a few times.
This bug will give you vengeance cap in challenge modes.
This bug was around in original MoP. If it goes live, it will feel as though you have to use it because of how strong it is and how it trivializes content. This is how brewmaster/disc can and did 2 man and time certain gold CMs. This is how all of the best times will be posted for challenge modes - incorporating this bug.
Tried to include a video clip but am not allowed to do so.