There are only two instances i know of where the Batman, whether it be Bruce under the cowl or not, really had a good laugh. Do you know who made the batman laugh? I bet you do, but first, let me tell you a joke.
"See, there were these two guys in a lunatic asylum... and one night, one night they decide they don't like living in an asylum any more. They decide they're going to escape! So, like, they get up onto the roof, and there, just across this narrow gap, they see the rooftops of the town, stretching away in the moon light... stretching away to freedom. Now, the first guy, he jumps right across with no problem. But his friend, his friend daredn't make the leap. Y'see... Y'see, he's afraid of falling. So then, the first guy has an idea... He says "Hey! I have my flashlight with me! I'll shine it across the gap between the buildings. You can walk along the beam and join me!" B-but the second guy just shakes his head. He suh-says... He says "Wh-what do you think I am? Crazy? You'd turn it off when I was half way across!"
Did you find the joke funny?
In most of the media where batman appears in, he doesn't laugh. The guy has no sense of humor. As Terry McGinnis puts it, "He wouldn't know a good joke if it bit him in the cape." Of course there is always a first time. If your answer as to who made the batman laugh is the Joker, how right you are. Who would be better at making the Batman laugh other than the Joke, right? I'm sure you found the joke above rather simple. Personally I didn't find it funny at all and to think a lame joke would make the batman laugh like a mad man, but the joker made the batman laugh with that joke. This is the first and only instance where Bruce Wayne as Batman laughed. You can read about this if you own the comic book, "The Killing Joke."
That's not the only instance The Batman laughed. I did mention a while back that i know of two instances where Batman laughed at the Joker. The 2nd one is Terry McGinnis as the Batman, when he laughed at the joker, not because he told a joke, but because Terry thought he was lame and pathetic. For those of you who don't know Terry, he is the new batman. Forty or so years in the future, Bruce Wayne got old and due to certain circumstances, a young boy named Terry McGinnis became Gotham's new protector. In this story, joker is long gone. Killed by an unstable Tim Drake (3rd robin, Jason Todd was the 2nd Robin, for a short time, and was killed by the Joker), after the joker captured and tortured him. Tim Drake was eventually helped back to sanity, but unknown to everyone, the joker implanted his consciousness in a microchip and placed it in Tim Drakes neck. This allowed the joker to occupy Tim Drakes body at will, even altering Tim Drake's appearance to look like the Joker's old self. As Batman (Terry) faces of with the Joker, occupying Tim Drake's body, one last time, Batman finds himself at the losing end. With Joker in Tim's body, he is able to fight the Batman with expert martial arts techniques. Its is here that Batman asks Bruce tips in fighting the joker. Bruce tells batman that the joker is vein and likes to talk and instructs him to block it all out and power on through. Instead of taking Bruce's advice, Batman starts talking to the joker which irritates the clown. Batman then gets a good laugh out of taunting the joker to the point of panic. "I'll laugh not because you're funny, but because i think you're kinda pathetic". Making the long story short, Batman was able to defeat the joker by destroying the chip on Tim's neck.
There you have it. The Joker made Batman laugh twice. First with Bruce Wayne, the original Batman, and second with Terry McGinnis, the new Batman.
By the way, if you've watched The Dark Knight, imagine Heath Ledger, as the Joker, telling the joke above to the Batman, Christian Bale. Do you think the Batman would laugh?