Vista banged Yassop's gf.
Yassop banged Vista's gf.
On a serious note. If they are related they would know about each other as much as Usopp knows about his fater. Which means they only know they are related.
There is one panel I think where they look at each other with this "satiric Huh?" on their faces.
Maybe they just got under each other skin in the past.
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They may have have a feud that started for a petty reason, or perhaps Vista has a special disdain for the ones who abandon their families, that he may be loyal to Whitebeard and his nakamas but that he would have never abandonned his wife and kid(s) if he had these.
The part about family is a good one. I like it.