Violent, Intense
When a yakuza's knife boils, you know something very violent and intense is about to happen.
The yakuza member is so upset his knife boils. Right after, they will definitely get violent and intense.
れつ
はげ
None
When someone gets violent or intense, they always yell "Let's (れつ) get violent and intense!"
In the case of our mnemonic, it's a yakuza member getting violent. So, imagine a yakuza member saying "Ret's get violent!" before doing just that.