  The spectral distortion of the cosmic microwave background blackbody spectrum
in a radially inhomogeneous spacetime, designed to exactly reproduce a
LambdaCDM expansion history along the past light cone, is shown to exceed the
upper bound established by COBE-FIRAS by a factor of approximately 3700. This
simple observational test helps uncover a slew of pathological features that
lie hidden inside the past light cone, including a radially contracting phase
at decoupling and, if followed to its logical extreme, a naked singularity at
the radially inhomogeneous Big Bang.
