I think Anthony also counts in this. Kenny could've easily just made his revenge about exposing Anthony for the bully he was or something, but he decided to give Anthony a year of pain. Talk about obsession.
Terry also specifically took a liking to Kenny without knowing about his history with Anthony. I think he can just sense it, you know?
Kwon also approached Sam unwarranted that one time. He was drunk, but people are the most honest when drunk.
I think it gets stronger the more a LaRusso ages.
Terry to Axel, "Only one of us is allowed to be obsessed with a LaRusso, and as your elder that's me."
lol