Before his formal training, Luffy released massive bursts of Haki during moments of extreme emotional distress.
But based on common fan discussions, most people asking about "Supreme Haki" mean the . So the clearest answer is: which episode luffy use supreme haki
, Luffy unintentionally uses it to intimidate Motobaro, Duval's massive pet bull. The Amazon Lily Incident: Episode 413 Before his formal training, Luffy released massive bursts