Curate, connect, and discover
I bet Chuuya was terrified of dentists when he first joined the Mafia.
Because like. He grew up on the streets. I doubt any of them ever exactly got health insurance.
So the first time Mori informed him what a dentist was and how often he was required to go, he actually freaked out.
Chuuya: what do you mean you sit in a chair and let a stranger tamper around inside of you?!
Mori: It's just your teeth, Chuuya, and it's required.
He won't refuse an order, so he goes, terrified. And the second he enters and sees the chair he immediately starts "Oh grantors of dark disgrace-"
Only for Dazai to show up because Mori made him tag along in case Chuuya tried to get out of it. He had to stand there the whole time, because if he let go, Chuuya's power would destroy the office on its own.
And even though he's become used to it by now, Dazai will never. ever. stop making fun of how terrified he was that first visit, nor will he ever let him live it down.
They're on a mission, and Chuuya's trying to be intimidating. Only for Dazai to tell the enemy, "oh, don't be scared of this chibi. He peed his pants the first time he went to the dentist." (he did not. or at least, he claims he didn't. We'll never know the true story).
Needless to say, Chuuya made sure that any enemy who Dazai told didn't live to share the info. Which may have been Dazai's plan all along, it's hard to say. Either way, no matter how much time has passed, Dazai still can't resist making fun of him for him once in a while.
And after the mersault arc, when Chuuya couldn't get the fangs out, he may or may not have said "Oh no, perhaps you should go to a dentist-"
Chuuya kicked him in his broken leg.