If I am at the gym with a buddy and he comes up to tell me that some chick just squeezed his guns, my likely reaction will be to ask him if she was hot (and if so we will probably high-five).
On the other hand if I am at the gym with a friend who is a girl and she tells me a similar story, my likely reaction will be to ask where the punk is because I'd like to have a word with him (actually first I'd probably ask if he was benching 300 pounds).
Of course there is a double standard. Men and boys on average do not have a sense of violation from those types of encounters the way that woman do. Maybe that is genetic. Maybe it is learned. Maybe it is because we tend to grow up rough-housing constantly. Or perhaps it is partly because we know that (in general) a woman can't hurt us if we don't want her to so we do not require the same level of shielding.
Regardless of the reason or reasons, we are different. If no double standard then who is to change? Do we want men to be offended by these types of situations? Why would we want someone to be upset by something that doesn't normally upset them? Or do we want women to be less offended by these types of situations. Personally I think we could all stand to be a little less guarded, but that can't be forced, nor can it probably happen with the world we live in today (unfortunately).
I tend to think that women in the scenario above would be upset more that another woman encroached on her turf than by any sense of her partner's body being violated. Look at it another way. Let's say it wasn't a boyfriend/husband, but just a friend. I just don't see many women being upset by that. I think most would just chuckle. Whereas, I think most would be upset if it was a female friend who had her butt groped.