Not really an impulse purchase, but rather an impulse decision:
Today I had a conversation with an English teacher and all of a sudden he asked me if I want to participate in the Chinese student exchange next year. He also added that I only have one day left to decide and I just replied yes, without even having any informations about it. Well, I'll just send in the application tomorrow and then, during this summer, I'll probably regret my decision one day. But whatever, from Europe to China and back again with a plane for only $400 together with a two weeks' stay in Peking shouldn't be that bad. At least I won't pay anything.
Jam it back in, in the dark.