retail bulimia
A condition in which a person shops incessantly, making extravagent purchases for the pure joy of the acquisition experience, but then returns everything the next day.
"I don't know what came over me - when I was in Nieman Marcus, I just had to have that $400 Versace bag, but once I got it home, I felt so guilty, and it seemed so ugly that I returned it.  After that, I felt great - cleaner somehow.  I'm afraid I might have retail bulimia."