Well, consider the name BLUFF-ing. He isn't serious...
It is actually two things. One, to a large macaw, this is a quite frequently a game. "HA HA! MADE YOU JUMP." This is how we institute beak wrestling...
BUT
It's also a way of saying this is my territory, and you are getting too close, I'm not interested in touching right now,
OR
It's also a test. PARTICULARLY WITH MACAWS THAT HAVE DOMINANCE ISSUES... They are trying to see if by doing the big bad bird routine, they can push people around, who they can push around, and how far they can push them around...
NON-DOMINANT MACAWS CAN BECOME MACAWS WITH DOMINANCE ISSUES WHERE THE "MADE YOU JUMP" GAME IS TAKEN TOO SERIOUSLY BY PEOPLE, and the bird is suddenly taught that he can manipulate people's behavior to get his way by doing it, BITING MONSTERS ARE CREATED THIS WAY.
The answer? PASS THE TEST. If he lunges at you, put the palm of your hand up and beak wrestle. "You don't scare me, silly! But I'm more than happy to play with you!" THAT is what defuses the whole "macaw bluffing" thing.
THEY KNOW EXACTLY WHO CAN AND CANNNOT HANDLE/DISCIPLINE THEM.
THEY STUDY US... and sometimes know things we wish they didn't.
Does that help?!
Macaws are the worst offenders, usually, but they all do it.