Yeah I played some more before checking back here and FordGT is right. The Arm Break move just has to be done VERY slow and deliberate, or the prompts won't highlight. It was literally grab, wait for the prompts to come onscreen, strike, wait for the 1st LMB icon to glow, strike, wait for the 2nd LMB icon to glow, hold strike, and it FINALLY registers as successful.
That one kinda felt like geezer school. I don't recall any other moves having to be done that slowly. Honestly, if they wanted to slow it down to make you remember the sequence, they should have just stopped motion until you click the prompted button, continue motion, etc, for ONE Arm Break, then make you do 2 or 3 more at normal fight speed to progress.
I have Dim Mak now too, but don't really use it. I was hoping it would be useful on Grapplers and Armed Thugs, but being as you have to grab them to get it started, it's hard to use on them. I've had better luck double jump kicking the Grapplers and tossing dropped blades at the Armed Thugs. At least the game offers many ways to fight, kinda like Max Payne 3 in that respect.
The purse snatcher I was referring to I just ran after on foot and beat up. One of Roland's missions where Roland comes with you to get a guy that owes money and takes off running I ran into with the car we drove there in, but of course the game wouldn't allow that to stop him due to it being scripted otherwise.
BTW, I enabled 16AF in NCP via a SD profile as rec by someone over at the SD forum. Rain reflections look a bit more realistic that way.