passing fancy 

a novelty that captures the attention of the general public for a relatively brief period, until either people lose interest in it, or the next "big thing" comes along.

also, an infatuation or a temporary but intense emotional attachment toward an individual.

Just as the hoola hoop of the late 1950s, so too did the Rubiks Cube prove to be a passing fancy after it was introduced in the early 1980s.

I suppose Sue's brief relationship with Tim was just a passing fancy for her, as she's since returned to her husband.

passing fancy by Polo June 10, 2007