I love that Buggy, in that sorry state he was, basically called them mediocre pirates.
"But Buggy is mediocre too"
Well, yeah, if he had trained, he would have been strong.
But he knows what he is, and he is a pirate, a weak one, maybe, but ultimately a pirate, and Roger's former crew member.
He never trained to get better because he felt he didn't deserve it. He never thought of being big outside of the East Blue because he thought he was not good enough. And now these guys, who are stronger than him, come and decided (in his eyes) to be just mediocre?
And this may be the moment when he finally accepts he put himself down all his life. He always played safe because in his own eyes, he wasn't enough.
"Shanks had so much promised ahead of him, I gave up on my dreams"
Since Shanks was the promising one, the talented one, the strong one, Buggy put himself down. All for Shanks, but he forgot to tell Shanks about it.
Remember after he was given the warlord title he fantasized about becoming an Emperor and later King of the Pirates?
He didn't say that because he got carried away. That had been his dream all along
A childhood dream he is claiming back. It may be impossible, delusional, and complete madness, but he, in his desperate state, is taking a chance
They may hurt him and humiliate him again later, maybe that would happen, I haven't caught out with the manga yet, but, for this moment, Crocodile and Mihawk can't do much because, as much as they let him be Emperor just for show and as much as they use him for their own convenience, they are not the ones all those pirates are following. It's Buggy.
He is the one with followers. He is the one who is loved, and he is the one for whom hundreds of people would fight (and maybe even die for).
After the indignation and rage cools down, he probably would be scared again, but for now, he doesn't care.