n'avoir ni queue ni tête

to make no sense at all

This expression means something is completely incoherent or nonsensical, it has no beginning and no end, similar to English "to have neither head nor tail."

Son discours n'avait ni queue ni tête, personne n'a compris ce qu'il voulait dire.

His speech made no sense at all, nobody understood what he was trying to say.

The idea of something having no identifiable beginning (head) or end (tail) goes all the way back to Cicero, who used the Latin phrase 'nec caput nec pedes.' The French version has been in use since at least the 15th century.