Batman and Superman basically invented the classic superhero look of a muscular dude with black hair and a square jaw. The problem with that is the two of them look almost exactly alike; so much so that Clark Kent was once actually mistaken for Bruce Wayne - at Bruce’s own party.
The Superman: American Alien mini-series follows a young Clark Kent before his career as Superman. In issue #3, Clark goes on a trip to the Caribbean to get away from Smallville for a while and clear his head after his breakup with Lana Lang. However, the plane winds up crashing in the ocean. Clark saves the pilot and brings him to the nearest ship, which happens to be a yacht. When he climbs aboard, he discovers the passengers are having a party for Bruce Wayne’s 21st birthday - and they think he’s the guest of honor.
A few familiar faces show up amongst the partygoers, including fellow playboy and soon-to-be vigilante Oliver Queen and future serial killer Victor Zsasz. Clark tries to tell everyone that he’s not actually Bruce Wayne, but he can barely get a word in edgewise. Fortunately, a girl named Barbara Minerva comes to his rescue. She pulls him aside and reveals she already knows Clark isn’t Bruce. “Bruce Wayne is never at his parties,” she says. “Trust me. I’m at every single one…No one’s seen Bruce Wayne since he was 12 years old.” It’s then Clark puts together who Bruce Wayne is and starts to worry he might get arrested, but Minerva reassures him that nobody cares. She even convinces Clark to keep pretending he’s Bruce for the rest of the party, which he does - and has the time of his life.
As a farm-boy from Kansas, Clark has never experienced such luxuries before, and while it’s fun, he also finds it hard to connect with these people. When he’s eating caviar covered in gold flakes with Oliver Queen, Ollie tells him each bite is worth four thousand dollars, and Clark can’t help but think about how that money could be put to better use. Minerva is the one person Clark does get along with. She actually helps Clark come out of his shell by talking about all the places she’s visited, which makes Clark realize he doesn’t want to spend the rest of his life in Smallville. This realization inspires his move to Metropolis and, eventually, his decision to become Superman. Thanks, Minerva.
But every party has an uninvited guest, and this one is no exception. When Clark starts to feel drunker than usual, he goes to the bathroom and finds Deathstroke there waiting for him. Slade was apparently hired by Carmine Falcone to assassinate Bruce Wayne and put a neurotoxin in the champagne to kill him. The only problem is, Clark isn’t Bruce - and he happens to be Kryptonian. The toxin does little more than make Clark dizzy, so to finish the job, Deathstroke decides to use his swords, which break against Clark’s skin. Needless to say, Slade is very confused, but Clark makes short work of him by literally flicking him off the boat. It wouldn’t be surprising if, after that encounter, Slade goes on to believe that Bruce Wayne is actually the Man of Steel.
Speaking of Bruce, the issue does provide a brief glimpse as to what he’s actually up to. In the last pages, Bruce is seen training with the League of Assassins when R’as Al Ghul shows him security footage of Clark on the yacht. Bruce has no idea who he is, as Superman and Batman's friendship hasn't been established yet. But, one thing is for sure, the two look eerily similar without costumes.