3) It's in refusing to back down from what I believe in, and admiring/identifying with others who do so. It pretty much breaks my heart every time someone says Ned Stark from GoT/Asoiaf was stupid for acting the way he did towards the end of book 1. All I can think is 'but he was doing the right thing!!1'. The outcome doesn't change anything about that. If anything, it makes his integrity more amazing imo.
I'm not completely sure if integrity falls into Gryff or Puff territory more, but the rigidity with which I hold on to my own (sometimes crazy strict) standards for myself made me question the lack of Gryffindor I used to claim.