Hmmmm ... I just reread this entire thread having been absent from it for a couple months. Some thoughts ...
First off, I see an awful lot of overreaction going on in the responses ... and most wouldn't be either helpful or appropriate to the situation the OP described. It makes me wonder if, culturally, we've forgotten that the whole point of scuba diving is to have fun, and perhaps socialize with people who share a common interest. It's a recreational activity, folks ... is there really a reason to attack someone or make them feel put off because they did something they probably thought was being helpful but in a way that you didn't particularly like? How about "handling it" by simply being honest ... and perhaps polite (like our parents taught us at an early age) ... and saying "please don't do that"?
The OP is from my area, and although diving's a pretty popular activity here, we tend to be a community who more or less know each other. My guess is she's diving with a dive club ... we have several in our area ... and the person she's describing is an old-school guy (we have a lot of those here too) who grew up in an era when diving was male-dominated ... and he's simply doing what was, in an earlier era, culturally accepted as "normal". If so, a polite response is more likely to change his attitude than an impolite one ... since the latter may give him more cause to consider the respondent's behavior than his own to be out of line.
Another thought is that, since she indicated they've dived together before, she may be demonstrating things ... perhaps without even knowing it ... that "ring some alarm bells" ... and without wanting to bring those things up he's just trying to make sure she's OK before going into the water. I'm not suggesting his behavior is justified ... but it is most likely well-intentioned. And a better way to deal with it would be a simple, frank question "Why did you do that?"
In today's society it's often difficult for a man to know how to interact with a woman on a social level ... because of our changing social expectations, certainly ... but also because (stereotypes notwithstanding), what one person may take as a compliment someone else may take as insulting. An example would be that I've known women who get insulted if a man opens a door for her ("I'm perfectly capable of opening my own door"), while another woman might get insulted if he doesn't. The woman in my life really likes me to open the door for her ... and she's one of the most capable women I've ever met.
Finally, for the guys out there ... a woman generally likes to be asked. I recall when I first started diving with TSandM, and was helping her become familiar with the BP/W setup I loaned her. I was real hesitant about helping her with the crotch strap. I asked her if she minded if I helped her with it, because of where it was. She said something like "as a doctor I don't worry about things like that." My reply was "as a scuba instructor, I do". I imagine that, even under the circumstances, not asking might have evoked a different interaction ...
... Bob (Grateful Diver)