The office of tribal Liar.

His name was Amschat B'hal Zoon. He lived on the raft with his three wives and three children. He was a Liar.
What always annoyed the enemies of the Zoon tribe was not simply their honesty, which was infuriatingly absolute, but their total directness of approach. The Zoons had never heard about a euphemism, and wouldn't understand what to do with it if they had one, except that they would certainly have called it "a nice way of saying something nasty".
Their rigid adherence to the truth was apparently not enjoined on them by a god, as is usually the case, but appeared to have a genetic base. The average Zoon could no more tell a lie than breathe underwater and, in fact, the very concept was enough to upset them considerably; telling a Lie meant no less than totally altering the universe.
This was something of a drawback to a trading race and so, over the millennia, the elders of the Zoon studied this strange power that everyone else had in such abundance and decided that they should possess it too.
Young men who showed faint signs of having such a talent were encouraged, on special ceremonial occasions, to bend the Truth ever further on a competitive basis. The first recorded Zoon proto-lie was: "Actually my grandfather is quite tall," but eventually they got the hang of it and the office of tribal Liar was instituted.
It must be understood that while the majority of Zoon cannot lie they have great respect for any Zoon who can say that the world is other than it is, and the Liar holds a position of considerable eminence. He represents his tribe in all his dealings with the outside world, their Liars.
Other races get very annoyed about all this. They feel that the Zoon ought to have adopted more suitable titles, like "diplomat" or "public relations officer". They feel they are poking fun at the whole thing.

From Terry Pratchett's Equal Rites