I always heard that as "I'm going for the Doornasty" Either way I knew to get out of the way.
That is amazing. That was the exact thing I have been hearing it as since the game launched. It wasn't until I looked it up today that I knew what it actually was.
I guess it makes sense because Mercy is clearly talking in another language when she uses here ultimate on the enemy team. With Zarya it just always sounded like English until the last word.