Superman is a bit too square to ever want a tattoo, but even if he decided to get an obnoxiously large “S” on his bare chest, is his skin too tough to tattoo? This is the Man of Steel after all, he can deflect bullets with a breath and survive nuclear blasts, wouldn’t a needle just bend against his skin?
Superman is the quintessential superhero and has a near-flawless sense of right and wrong. He is also pretty squeaky clean, especially through the lens of his alter ego, Clark Kent. The bespectacled newspaperman is as twee as they come and would never disappoint mamma Martha by adding tattoos to his unblemished skin. But if Clark ever had a rebellious streak, could he even get ink done since his Kryptonian DNA makes him invulnerable? And would he choose something tacky like barbed wire around his prodigious biceps?
Superman can be injured. Kryptonite (fragments of Superman’s home planet) is one of Superman’s few weaknesses. It’s been exploited again and again by villains (and sometimes friends) to level the playing field against the otherwise god-like Superman. He’s even died a few times, often as a result of blood poisoning from Kryptonite.
But just a regular old steel needle (like the ones in tattoo guns) isn’t going to do anything except break against Superman. At his most overpowered, Superman has withstood the intense forces in the center of the sun and even held a black hole in his hand. Tattoos need to cause a wound for the ink to seal in the skin, forming a sort scar that makes the tattoo permanent. In order for the ink to endure, the skin has to heal over the ink. Superman has no scars to speak of, because one of his powers include super healing. If Batman ever had a mid-life crisis and asked Superman to go get matching “best buds 4 life” tats, Superman would have to break some bat hearts.
The only conceivable way to tattoo Superman would be to either use a Kryptonite needle and inject ink that is laced with trace amounts of Kryptonite. Or, have Kryptonite nearby while a more traditional tattoo is performed. Either option relies on the hope that Superman’s body creates scar tissue to make the ink permanent. But given that Superman has no scars to speak of, any kind of tattoo is probably impossible.
Superman heals up as soon as Kryptonite is removed from his system. If the needle was made from his home planet, the tattoo still wouldn’t take and the ink would likely just reabsorb once he heals. If the ink was laced with Kryptonite, Superman would be permanently weaker and could potentially get blood poisoning and die. But he would have some sick permanent ink. While getting a tattoo is possible, Superman wouldn’t likely take the risk by injecting himself with Kryptonite-laced ink, regardless of how cool a font he chose for the words “Man of Steel” to go across his abs, Tupac-style. The best Superman can hope for is those washable temporary tattoos that anyone can use.