(perhaps a SPOILER)
I just saw the begin of the sykpea arc on german tv, and when ace met buggy, buggy realized that ace is a member of the whitebeards, ace said: ah... so you know my father .... So... is this a translation error or what?
Cause in the english tanslation, ace says : so you know our old man.
This could explain why aokiji had already met Luffys grand-father, and why Luffy is not so amused to speak about him.
What do you think?