While not known for his sense of humor, Batman certainly got a big reaction from the Justice League at the end of this issue when he made this joke. It was a vampire related pun, and his cohorts were more shocked than amused, but everyone starts somewhere.
In JLA #99, jointly credited to John Byrne, Chris Claremont, and Jerry Ordway, the League finally tracks down Crucifer, the leader of a vampire terrorist group known as the 10th Circle. Crucifer and his minions have an aggressive agenda to infect metahumans in order to breed a race of super-vampires. When the latest attack turns out to be a trap laid by a young girl named Nudge, the Justice League are led back to an old ally.
Nudge works for Niles Caulder and thus, the Doom Patrol join forces with the JLA. Even though the styles of the two teams clash at times, their knowledge combined leads them to Crucifer's lair. The head vampire is weakened when he bites into the Martian Manhunter disguised as Wonder Woman. (Martian blood is poison for these vampires). After that, it was a simple case of a wooden stake through the chest. This was what caused Batman, in the very last panel, to cooly remark, "it's a good thing his heart was in the right place."
Aside from the Dark Knight trolling his teammates with bad puns, this team up also pairs the Atom with Rita Farr from the Doom Patrol really nicely. She uses her size-shifting powers to follow Ray Palmer into a side dimension only accessible by pocket talisman, and the two destroy one of Crucifer’s assets that way. Juggling both super-teams left a little bit to be desired as far as character balance and interaction, but at least moments like those lay some future groundwork.
This mission, mostly conducted without Superman, meant that Batman had to step up and take more of a leadership role, ordering troops around, and taking point on solving the mystery of Crucifer’s location. After all of that assertiveness, and a group dynamic that was honestly skewed far more toward tactics than camaraderie, it was nice to have Batman lighten the mood at the end with a joke. He’s no Flash, chatting it up in the middle of battle, hoping to off-put his opponent with a quip. But, at the end of the day, when his team has earned it, even Batman’s not above a little self-deprecating Dad-joke.