How do you think the Bracken/Blackwood feud manifests itself? Obviously we have the siege of Raventree Hall and taking opposite sides in wars, etc, but in relative peacetime?

We’ve got plenty of historical examples: 

• the private war between the two houses in -10 AC. 
• the duel over the hand of Rhaenyra Targaryen in 112 AC. 
• the Brackens and Blackwoods engaging in rival dynastic politics during the reign of Aegon IV.
• Otho Bracken killing Quentyn (boy, there’s a name that’s just a death sentence in ASOIAF) Blackwood in the King’s Landing Tourney of 206 AC.
• The legal case of Bracken v. Blackwood before Hoster Tully in the 270s.

But most of all, there’s just constant private wars: “We’ve had a hundred peaces with the Brackens, many sealed with marriages. There’s Blackwood blood in every Bracken, and Bracken blood in every Blackwood. The Old King’s Peace lasted half a century. But then some fresh quarrel broke out, and the old wounds opened and began to bleed again. That’s how it always happens, my father says. So long as men remember the wrongs done to their forebears, no peace will ever last.“

A hundred peaces means a hundred wars, scattered across six thousand years of history. So every couple of generations, low-level tensions build up and up until there’s a proper war and then it’s off to the races.