Having Perona and Zoro around for a time helped bring Mihawk out of his cocoon a little. As a result, he doesn't mind partaking in some company once in a while.
That doesn't change once he's with Cross Guild. He still keeps mostly to himself, but if there's nothing important happening and he's bored enough, he'll step outside to go and see what the Buggy Pirates and their clown captain are doing. He observes for awhile, has a drink, maybe chitchats with someone.
Soon enough, Buggy learns Mihawk likes to indulge in music.
Buggy learns Mihawk will listen to almost anything with them.
Buggy learns Mihawk knows every word to Bohemian Rhapsody and will silently mouth them along while the rest of the Buggy Pirates are belting them out like drunk dying animals.
Buggy learns Mihawk will bang his head right on cue with the rest of them on that rockin' guitar solo.
