How fast does a car have to be going destroy Lexus rear bumper?

It depends on various factors such as the type of Lexus model, the specific rear bumper design, and the construction materials used. In general, to cause significant damage to a Lexus rear bumper, the car would need to be traveling at a sufficiently high speed to generate enough force upon impact. It would also depend on the point of contact and the angle of the collision. Without specific details, it's difficult to give an exact speed at which a car would destroy a Lexus rear bumper.