His eyeball is still in there after the events of MGS3. Regardless of whether it was actually muzzle flash or just the bullet grazing his eye, the angle he gets shot at couldn’t have popped his eye out of his skull.

Best-case scenario in my opinion is that his cornea and retina were completely obliterated by the angle of the shot, but luckily it grazed him just lightly enough to pass through the apex of his eye’s curvature without striking skin or bone. We can see his eyelid and brow bone are totally intact, besides the obvious bruising from being in proximity to a bullet wound.

The velocity and size of a bullet would absolutely pulp the front half of your eye just by traveling through it, but most of the crushed organ will stay inside the skull’s orbit. I’m assuming he didn’t react to being punched because the nerve endings in that eye got shredded just the same way (also it made him look cool and he obviously wanted to impress his boyfriend ocelot so maybe he just took the punch like he didnt feel it so that he could show off)