Eu recebo este erro:

java.util.regex.PatternSyntaxException: Look-behind group does not have an
    obvious maximum length near index 22
([a-z])(?!.*\1)(?<!\1.+)([a-z])(?!.*\2)(?<!\2.+)(.)(\3)(.)(\5)
                      ^

Estou tentando igualarCOFFEE, mas nãoBOBBEE.

Estou usando o java 1.6.