snapping boxer

Question
My boxer Tyson is 7 years old. He was given to me when he was 6.  He was raised in a loving home and taken very good care of.  Since I have had him he has been nothing but loving and playful with my husband an i as well has our Pekinese (SP).  Here is the problem,  he has growled and snapped at a couple of my girlfriends.  One of them was petting his face and he snapped at her.  The other one, on a different day,  simply asked him to shake (which he knows and has always done)  she did not touch him she was not aggressive by any means  and again he growled and snapped.  As if that was not enough when I looked at him and told him "no" he snapped at me.  He has NEVER done that to me.  What could be triggering this behavior.   Thank you for your time

Answer
If he's not fixed,getting him done may reduce aggression

It sounds like you are dealing with a dog that is dominant and a good way to solve this is to take him to obedience classes,not only can a trainer work one on one with you,but it will put you in charge-and not the dog,this can become a serious issue if he moves from snapping,to biting

It's dominance that is causing this problem-he growls at you for telling him off,because he is trying to get get you to back down from him,because he views himself as the leader,and not you,and the best way to put yourself at the top is obedience classes,even if he did have them with someone else,by you taking him it puts you at the top of the pack