To state the obvious, this is NOT COOL.
I agree that there are a couple of problems here:
#1 The guy hitting your chest. A number of the existing suggestions are great. The one I like best is directly addressing it with him and asking him to direct his punches elsewhere. If you don't get any cooperation, don't train with him. There is no need to encourage him.
I'm also not against the idea of having another guy tell him. We have some senior students at my school who are very good at pulling other students aside and "giving them a heads up." While as the instructor, I tend to handle things personally, I know that often other male students, especially advanced ones, are glad to help out their classmates.
If he hears it from them, and then you address it directly, he will know that he really needs to take heed.
#2 The instructor. This could be a bigger problem. If he doesn't have your back, you may not be training at the right place. His job is not strictly to disseminate information. His role is to have the final word on any and all things that happen in his school. The school is an environment that he creates and maintains, and he bears full responsiblity for it.
If he's just encouraging you to be assertive, that's one thing. If he's dodging the topic because it's awkward, or because he doesn't see anything wrong with it, then he is the biggest culprit. That's a major problem.
Handle the student first. That's the short-term problem. After something happens, whether it is effective or not, it's a good time to check in with your instructor. Tell him what went down. Get his feedback. If it was a success and he's proud, then good. Maybe he's OK after all. If he is indifferent, or if you were unsuccessful and he's still unwilling to help, it's time to make it plain that he isn't keeping up his end. And if you don't get a response from him, it's time to go shopping for a new school.
As an aside, I have 2 BJJ programs I oversee. In one, it is mostly guys. In the other, it is mostly gals. In the first, I occasionally teach 2 versions of a technique (at the same time), if one of them is a little "gender-awkward." For example, one night I had only myself, a 16-year old girl, and a 40-year old guy. Now, the two of them are friends, and there's no weirdness between them, but one of the moves we worked involved kneeling over your pinned partner and squeezing their head between the knees. Needless to say, some modifications were offered for times when you didn't want to go that way.
The job of any instructor is to keep his students safe at all times when in his classes. This is not just from physical harm.
~TT