Then we're describing the same thing. But to me it's not an "impulse" as much as a premeditated thing that kinda gnaws at the back of your mind for a while.
I think that most people on here would think an impulse buy is sort of a "I just saw this for the first time and I have to have it" kind of thing. Which definitely DOES happen. Especially around 3 a.m. on a Friday night. heh-heh
But I understand what you're saying now.
Just a subtle difference in word definitions between us.