Klaus and Stefan have agreed they never want to talk about Caroline, about Stefan’s past with Rebekah, about Stefan’s ripper past and Klaus’s role in that, because they would rather concentrate on their future together instead of their rivalries of the past.

Jeremy and Kol never discuss the fact that when they first met Kol wasn’t being honest about who he was, or that Klaus had engineered their friendship in the first place; Kol’s previous death at Jeremy’s hands is also never up for discussion.

Alaric and Damon had agreed from the start they would never talk about Isobel; Damon would prefer it if Alaric quit bringing up the times he’d killed him every time they have an argument; before Damon took the cure, neither of them ever wanted to hear any mention of the fact that Damon was immortal and would go on living his undead existence long after Alaric had crossed over.