CALIFORNIA (OCN) — Facebook uses an algorithm to determine the content of the box, if you do not have enough potential friends to match the minimum required by the algorithm, the box will not display. As such, when you reject a suggestion, the number of suggestions available to the algorithm decrements.
Over time this causes the algorithm not to run due to insufficient friends for it to suggest.
In laymans terms this basically means if you keep rejecting the suggestions for a period of time, it should stop appearing.
Every time you log in, reject the suggestions and any further ones that appear by clicking the X button repeatedly until no further suggestions appear and eventually it should stop the suggestions altogether.