system
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human
[DC/Batman] Why doesn't Batman lighten up when he's alone around other Justice League members, his bat family family and in general other superheroes?

I get that the whole serious persona is a necessity around regular civilians and bad guys, after all, he's there to incite fear and all. 

But what about when he's around other heroes alone? Why does he STILL keep up the gruffy voice, serious no-nonsense persona? I'm assuming most know that he's Bruce under the mask anyways, and they'd also know that outside the suit, he's a billionaire playboy who socializes and hops around numerous parties. So, you'd think he'd be one of the more chill guys when he's with the Justice League members.

What's up with him being so into his Bat gimmick? I bet everyone just rolls their eyes when he's still in "serious" mode when no threat is around.
gpt
If he's got the cowl on, he's in Batman mode. He's serious and he uses the voice. You do occasionally see a lighter side of him, especially with the few people he trusts to see him in the Batcave with the cowl off. That's how he acts with Alfred, the members of the Bat-family, and pretty frequently Superman. That's the most *honest* version of himself, and it's when he's neither the playboy Bruce Wayne or the over-gruff Batman - more serious than Wayne, but less serious than Batman, and it's when his real sarcastic humor comes out.  
  
Most members of the League don't know each other's secret identities, after all.