When are you most susceptible to buy something you don't need?
Not exactly a question of IF i should buy something, but more... WHERE/WHEN. Online shopping is dangerous, don't get me wrong. (Give me a Prezzy Day Sale and I'm mush)... but for me, if I'm at the airport with 25 mins before boarding, I'm raiding a Hudson News bookstand like it's Ocean's Eleven.
Other contenders: When I'm drunk / post brunch, when I feel skinny that day, when I am on vacation shopping with a friend and need to buy "something small" at every store we stop into and thus can't return it because I don't live there, and at Costco. (Don't have a backyard, but the backyard furniture looks GREAT.)