Imagine being in a state of ecstasy, constantly from start to finish, during a battle must be terrifying for Luffy's opponents
Imagine a dude GENUIENLY laughing, giggling and making fun of you in a battle where powers that destroy literal buildings are colliding and haki that would make an entire island worth of people pass out clashing
Luffy isn't taking anyone seriously, joking around and doing shit for fun.
It get so fucking scary when he gets serious. He's still smiling mind you. But he's got that dangeous glint in his eyes constantly now instead of random moments of it appearing.
Red eyes setting off the alarm bells in your head and his giggles probably sounding like hearing a child laughing in an abandoned forest while you're alone in there.
NOT TO MENTION THE FUCKING DRUMS. Just. Random ass drums start playing. You are in a fight that will probably destroy you. And there's fucking music randomly playing in the bg.
The fact that only Luffy could use this fruit to it's true potential. If he didn't believe in his freedom, if he wasn't a silly little guy, he would not be able to awaken the fruit. It's the most ridiculous power, because it's so unserious and that's why it fits Luffy perfectly and no one else.
And of course, before him only Joyboy was able to awaken this power too.
"these things cannot be stopped; an inherited will, one's dream and the ebb and flow of the ages. as long as people hunger for freedom these things will exist" - Pirate King, Gold Roger chapter 100