It is said that the term originated in rodeo, where steer wrestlers would encounter a steer whose neck could bend at absurd angles. This made wrestling the steer to the ground a lot more difficult, because bending the neck was important in getting it down. The cowboy might not be able to complete the maneuver in the alloted time. The excuse would be that the steer had a "rubber neck." It was not meant kindly. These days the term generally means to look about in unsophisticated curiosity.