See, I think THINKING about it is fine. THINKING, "Stuff you, I'll go do it anyway!" after an argument about it is probably a fairly normal reaction to have. Thinking about it in a day-dream sort of way is fine too. I think it's normal to fantasize about getting what you want.
Actually going through with it is another thing altogether though.
I often talk of all sorts of things I'd never actually do - smashing into some idiot driver in front of me, sticking a cork up DP's backside for endless farting (lol), telling that b*tch at work exactly what I think about her using as many colourful words as I possibly can... but actually going through with it is so different from thinking about it.
It's that GOING THROUGH WITH IT that takes a normal adult to a deceitful, selfish, immature jerk.