As an instructor as well, I tend to agree with Chickdiver on this one. I tell students up front when I may have occasion to touch them and where the touch will be. If they indicate that it's okay, then we proceed. If not, then I go to some alternative plan. Don't know what the alternative plan is, because no one has objected.
In my opinion though, in a valid rescue situation, all bets are off. I will do anything in my power to save the life of a victim and in the process if something is grabbed, held or touched, such is life. If they want to state their objections after they've been rescued, they are more than welcome to. I will just be happy just to hear their voice, no matter how shrill it is.
But outside of a rescue situation, then any touching outside of 'normal' attention getting or what have you, is not appropriate - not in the least! If I saw a DM that was working for me touching a student or a guest in a manner that wasn't right, he (or she - let's be fair here) would have some serious explaining to do, followed by a sincere 'I'm sorry' to the individual and probably would not dive with me again. It's just not worth the bad reputation I would receive.
If this stance offends anyone, I'm sorry, but that's how I feel. Have I rescued women? Yes. Were things grabbed? Yes. Was anything said? Yes - heartfelt thanks and tears of gratitude. But I have never, nor will I tolorate anyone taking advantage of a situation on my watch.
Simply my 2 cents worth.