CP0 showed up in person to make deals with Orochi because Doflamingo was gone. Mingo knew how useful he was and was flexing, which is consistent with his character. He freaked out seeing a glimpse of Fuji's power, but tries to kick him and plan his downfall when he now knows that latter is passive. He also panics at the idea of angering Kaido. He also thought:
-he could kill Smoker Infront of Kuzan
-that Vergo could handle Luffy and Law
-that Daimante could handle Luffy and Burgess
-that him and family can handle Fujitora with a plan
-that Pica alone can handle everyone in Dressrosa including Fuji
-that he can overpower KKG head on despite failing multiple times
He's just as arrogant as arrogant can be.