actually, technomancer is right.
there are a LOT of methods to doing the gentleman.
the ones i know are
1) the timing method. press A, pause, press A and pause, and finally press A and pause. this method is the ONLY one that works if the first punch does not connect. it is slow, shieldgrabbable, and should not be your main method of doing a gentleman
2) plain o'l AAA
3) light shield AAZ
4) the combo, AA A+Z
5) the tilt, AA forwardA
the last 4 basically all do the same thing (except some put up a light shield and others do not). they can all work or not work based on the exact same reason. i can make every on of these methods work and i can make every one of these result in a rapid punch.
the way to make it work is the 3rd button has to be pressed AFTER the second punch has already connected.
the real secret to the gentleman is in the timing of it. the way to do it as fast as isai and spectre and them is to press the first 2 punches as fast as you can, AA. then you need to time the third hit, and it helps to hold the button down longer.
the idea is to play around with all those methods, and find which one helps YOU to time it. personally, i AAZ, i like the light shield, it gives me some semblance of protection after doing a great defensive move.