One of the biggest handicaps with a foreign language is not being able to insult a man in his own language. Or worse still, not being able to defend yourself against an insult.
Indeed, practically all the bad words in English are German in origin, but we'll come back to this again. Insulting people is (hopefully) not one of your core activities, but there comes a time at least once every year when what's needed is a sharp word or two to prick the pomp of that idiot. The trick here is not to show the least amount of emotional annoyance. This would only betray the fact that the idiot has indeed got under your skin. Best to veer towards shades of indifference, like Robert Louis Stevenson did when he said: "I regard you with an indifference closely bordering on aversion."
This was also the tactic of Oscar Wilde when he said of George Bernard Shaw: "He hasn't an enemy in the world, and none of his friends like him."
Another option is understatement, as when Winston Churchill said: "Mr Attlee is a very modest man. Indeed he has a lot to be modest about." Retorting to insults is a skill in itself, as when Pierre Trudeau replied to Richard Nixon: "I've been called worse things by better men." And remember the words of Groucho Marx: "He may look like an idiot and talk like an idiot but don't let that fool you. He really is an idiot."