The most unrealistic scene for me so far is Dylan beating a bum after two days of training, in front of the bum's friends and they walking out like they were scared of the little guy.
I don't consider that unrealistic because what Dylan did does not actually show he is good a martial arts. Let me explain.
First, Dylan caught the hobo off guard, naturally a huge advantage. Generally catching someone off guard is more than enough to win a fight.
Second, Dylan used a set of predetermined and practiced moves, does not show that he is actually a trained and good fighter ( at least not a trained martial artist ).
If Dylan's move was blocked and countered and if he was still able to counter back and win the fight then you could say that it is unbelievable, because blocking and countering someone in an unexpected attack is what martial arts training actually helps with and that's what requires actual skill
Thirdly as far as I remember he hit him on his nose which is a very weak spot, even the strongest men would feel weak after a good hit there.