You should be taught professional touch the first week. You'll see every one of your classmates with their shirts off at some point, but almost everyone in the room is self-conscious and not thinking about what you look like, because they're worried about what they look like. Your classmates will range from very heavy to extremely thin, and everything in between. Some people have had surgery in the past & have scars, some will have religious reasons why they can't show too much skin, etc.
I learned a lot in OMM & our hands on doctoring course about how to make someone feel at ease in an awkward situation, how to behave professionally, how to ask people to move or shift body parts without sounding weird ("Can you please lift your left breast so I can listen to your heart?"), how to respect people from other cultures who have to work around religious regions for not being undressed or needing a female partner, how to delicately ask about scars, tattoos, etc. Even if you don't use OMM after medical school, I think there's a lot to be gained from the hands-on aspect of the class.
It really bothered me at first to have people touching me, especially guys in class. I've been married a long time, and I tend to have a large personal space bubble anyway, so taking my shirt off in front of a guy I didn't know and letting him touch me (even on the back & completely professional) just felt so wrong at first. But then I started thinking about how our future patients might feel the same way when we're going to examine and/or treat them. They'll feel awkward & uncomfortable letting a stranger look at their bodies and touch them, and having had to experience that myself will hopefully help me put them at ease in the future.
Edited to add: if you (or anyone else) has ever had a spinal injury or back/neck surgery, you need to go see your OMM course director ASAP when you start school. There will be techniques you can't have performed on you, and if they know in advance then accommodating those needs will go a lot smoother for you.