It is possible that if you grab a woman by the arm in just the right way you can touch her breast. My college professor was keen to stand behind us while we were in computer lab and to help us would bend over our shoulder so her breasts would be in contact with the upper part of our back. A couple of guys in the class commented on that and some other things she did. Those were some fun days! /s
In the case of my colleague with the 42-D cups I suspect it was impossible to touch her arm and NOT make contact with the breast.