Have at it!
Anyone with a gun, for a start.
MacGyver.
A shark.
Any number of foes have beaten the Batman in the first round. There was the guy (name, anyone?) who had a cybernetic implant that allowed him to instantly download fighting skills that ordinarily take decades to acquire. He wiped his ass with Batman the first time they fought; and Batman only won the second time because he found some sort of trojan or crack that would disable his opponent’s implants.
Almost anyone with actual super powers, like the rest of the Justice League, for instance.
A Bear.
Chuck Norris.
Almost anyone with actual super powers, like the rest of the Justice League, for instance.
An orang-outang.
Alternatively, almost anyone with actual super powers, like the rest of the Justice League, for instance.
A jar of pickles.
Also, almost anyone with actual super powers, like the rest of the Justice League, for instance.
Prometheus. It wasn’t implants, just a helmet. Batman disabled him by swapping his ‘20 Greatest Fighters’ disk out for one with the physical skills of Stephen Hawking. (I THINK it was 20…it contained Batman, Richard Dragon, Lady Shiva, and others.)
He smartened up, after that, and when Oracle recently tried to hack the helmet, he destroyed her computers.
Many of the other people on Prometheus disk - Dragon and Shiva, specificallly - could take Batman in a straight fight, if they didn’t give him a chance to swing the odds. Superman, assuming he turned evil and took Batman by surprise could take him out - and has, when mind-controlled in the OMAC mini. Flash, Wonder Woman, J’onn J’onnz, hell, even Aquaman and Plastic Man could. Firestorm, Deathstroke, Green Arrow with the further training he’s demonstrated recently, Metamorpho… I’ll cut this short - nearly anyone with superpowers, and a couple capes who don’t.
Leaving the DCU:
Midnighter, or most of the rest of the Authority.
Spider-Man.
Half the characters Arnold Schwarzenegger’s played.
It depends on what kind of contest. In a hot dog eating contest, Takeru Kobayashi could defeat Batman easily. I bet an unprepared Batman couldn’t beat Tiger Woods in a head to head golf match (no handicap). Hell, I bet Serena Williams could wipe the court with him at Wimbledon.
If you’re talking a no-holds-barred battle royale, I’m pretty sure The Incredibles could kick his ass.
And, possibly, the other folks in that crime-fighting organization that has a roster of superheroes. I’m blanking on the name of it, though.
“Alfred, I feel woozy”
“That, Master Wayne, is because I have taken the liberty of spiking your tea with a mixture of the poisons you haven’t built an immunity to.”
Cecil Adams.
Jack Bauer, preparation be darned.
For my money, it would be almost anyone with actual super powers, like the rest of the Justice League, for instance.
I’d actually like to see Conan vs. Batman. One’s all planning, one’s all reflexes and instinct.
Captain America (kidding, don’t wanna start a huge debate).
Any of the Flash’s Rogues.
If he’s not prepared, I can kick his ass.
I notice nobody has mentioned Robin. That may be the only comic book hero who Batman could defeat, anytime, anyplace, prepared or not.
As for who could defeat Batman, well, there’s Superman, Wonder Woman, Flash, Green Lantern. . . hell, a whole league of American superheroes, as long as they’re dedicated to justice.