I don't know about most powerful, but they are intense.

GF - "sonofabitch" - Sonny Corleone when he sees Connie beat up.

GF2 - "Morte" - Frankie P. tell Michael how he wanted the Rosatos.

GF3 - "Bastardo" - Joey Zaza whispering in Vincent's ear


Whoever exalts himself will be humbled, whoever humbles himself will be exalted - Matthew 23:12