Is it a valid consonant cluster in Lojban?
Pyth, 53 48 47 bytes
!}z+&quot;mz&quot;s.pMs[+VGGc&quot;xcxkcsjz&quot;2*&quot;ptkfcsx&quot;&quot;bdgvjz

This generates a list of all invalid pairs based on the rules above, then checks if the input is one of them.
! }                        A not in B
    z                      input
    +
      &quot;mz&quot;                  &quot;mz&quot;
      s                    flattened
        .pM                permutations of each:
            s [               flatten the three-element array:
                +V              Alphabet vectorized concat with itself.
                   G            That is, duplicate letters
                   G
                c&quot;xcxkcsjz&quot;2     That string chopped every 2
                *               outer product of
                  &quot;ptkfcsx&quot;      voiced letters
                  &quot;bdgvjz        and unvoiced letters

Try it here.