Typically my new gun purchases are well-conceived in advance, meticulously planned, and carried out to perfection. Fulfilling as I get the gun I want but the "hunt" is not nearly as exciting as finding and buying something impulsively.
Impulse buys for me are much more random and usually occur while looking through the Used Gun display case at the local gun shop or while making the rounds up and down the aisles at a local gun show. Over the years I have become much quicker at making my "impulsive" decision to buy something as I remember all too well the ones that got away because I took too long to make my mind up or else I wanted to do a more in-depth study of the gun before getting it.
Some of my more spontaneous buys were a S&W Model 34 that was like new in the box (at a great price), a Baby Browning that was also mint in the box (another one at a fantastic price), a minty Browning Model 1910/1955 (super deal on this one too), a very lightly used SIG P229R with SRT, E2 grips, night sights, and three extra mags (all for less than half what a new one would go for), and a Colt Model 1908 Pocket Hammerless in 99+% condition with factory nickel plating and factory pearl grips with Colt medallions on them (it also included a Heiser "pocket holster")! Admittedly the last one was a trifle more expensive than any of the others but well worth it!