if they try to do this again, might I suggest a few methods that will make them let go? if you pinch the skin between the thumb and index finger, and use your fingertips, you can bring just about anyone to their knees. if they grab your arm, and your other arm is free, grab their thumb and push it back, towards the wrist(the part where the face of a watch would be, assuming you wear your watches with the face on the top of your arm), but be careful, you don't want to break it unless you have to. once again, this will bring just about anyone to their knees. I once brought the biggest guy on my HS football team to his knees using the thumb one. I am 6ft, about 170, and he was 6' 9" easy, weighing about 270, almost all of which was muscle. after I did that, no one ever messed with me again. usually, if you can get one down, they will back off, because no one wants to be next.
[EDIT]These moves also come in handy if you are trying to rescuse a person who is drowning, and they attempt to force you under to keep their head above water(they do this quite often, in a panic I'm told).[EDIT]