"Did you see that? Superman just caught that bullet in front of me. No, seriously. That blur was Superman. He's amazing!"
Few people, watching someone get shot in the face, are going to accurately and with total surety recall what the impact looked like. That Superman zipped by and stopped the bullet makes more sense than Clark suddenly being invulnerable or something.
And, if that fails: Mxy did it. Goofy lil dude.
More guaranteed way to kill Superman:
*Leave a letter explaining she's been dropped into the harbor in a barrel
*Superman flies beneath the water to save Lois.
*He tries to scan the barrel to see if Lois is in there, but it's lead-lined. He can hear her heartbeat, though, so he opens the barrel
*A kryptonite-shrapnel bomb detonates, impaling him in the face, neck, and chest with jagged shards of kryptonite
*Lois is killed in the blast, and Superman dies shortly thereafter
I'd be more worried about people bumping into Clark in crowded areas. He'd have no real way of avoiding it, and it'd be like going against a brick wall. Or Lombard trying to whack him from behind as a prank with no warning, and hurting his hand. Or even something as simple as someone grabbing him by the arm - I can't imagine Superman's super-dense skin having that much give, after all.
When Clark relaxes his body and relies on his reflexes, then he's able to roll with any movement. Meaning someone can bump into him and not be hurt. When he tenses his body and stands still, then body parts are broken.
Armageddon 2001 was great. Just a bunch of near-future Elseworlds stories, basically.
Either he's missing a step or Superman opened the barrel in the water
(Although it's not something generally used in the comics (I can only, at the moment, recall it being used in the Kingdom Come novelization by Maggin, and I think it was used in the Alien crossover), Superman can use sound to determine a basic image of what is in the lead-lined barrel and would also be able to determine whether or not it was hooked up to an explosive device.)
lets assume the shooter is Deadshot and he does one of those crazy shots of his, even if the bullet bounces off Clark's face what the problem here? Before the shooter has any time to react Sups will already be on top of him catching him and taking him to the authorities so by the time the shooter is able to put together everything that just happened he'll already be in jail and even then so ONE person might have an idea that Clark is Superman, so what? Who's gonna believe him? What prove does he have?
Look my point is I can tell all of you right now how I'm dating Powergirl; but are any of you going to believe me? Even if ONE of you saw me with her, would the rest of the world immediately belief that person? And for the hell of it lets say that 1 person that saw me was a pedophile deviant assassin, would you still believe him?