That's funny since I have the opposite problem, I can't seem to get male physiques looking right even though I'm aware of the squareness of their build. I mean, my girls still need work tbh, but I draw them much easier than guys. Also, I have a hard time coming up with guy hair styles, but girl hairstyles I can come up with a dozen on the fly. It's weird lol.
Armpit placement is a unique example, actually, but I can see where you're coming from, Sometimes, I get confused as to which direction the concaveness of the armpit should be, even with the placement of a side-boob outline. I also have to occasionally remind myself shoulders are connected to the clavicle, so they need to be drawn on the same level and not just rounding out from where the base of the neck lies.