I think you’re right — body armor of some kind. He’s scared.

There's only one way to find out

Bullet resistant* vest

I think more like s bullet proof corset

That's not at all camouflaged.

With a completely exposed face?

Not going to do anything if the gunman aims for the head

Body armor typically covers from around the belly button to around the manubrium of the sternum. The reason I don't think the body armor thing is true true is because of the indents just under the breast/nipple area. Unless the vest is reeeally shaped like that, those curves would not show up. I think back to when I was wearing body armor and remember a pretty obvious line on the front portion where there was an obtuse angle formed as the shirt met the stiff portion and cascaded downwards, but no odd curves where the shirt was pulled tight after that, just wrinkles and folds where the fabric was loose.

Now, that being said, if this is super light body armor (and he's probably enough of an idiot to wear a level I vest and think it's enough), those might show up. The oddities on the back of the shirt do make it appear that something is going on underneath. The thick black line where the shirt is folding inwards could be because of the bottom of a vest, as it lies just around the level of the navel, as you'd expect with body armor. Just in front of the left elbow is another dark patch, which could be due to the fabric being pushed outwards around the location where the straps attach.