When you see a map and inform your friends that you once conquered great territories on that given map.
Very true, but it's not only CK2 that causes it, this is a very old habit. I'm pretty sure my wife enjoys hearing me say that, along with "I could build one of those" about, e.g. Spaceship Earth.
when you go and give your counsin a good tumble
I cant top that, however, I know I've been playing too long when I decide I need to take a break from the game, and go watch a let's play, or read JJN's Byzantium (short version).