The Queen's English

his biting sarcasm

Provided that it is done well, a really passionate speech is far more persuasive than a balanced one. If you are trying to convince your audience of something then a totally biased presentation often works best, whatever the ethics of it might be

Italian: many culinary and musical terms, such as pizza, al dente (cooked but firm) and lento (slowly); piazza (open town square). Of these, only al dente is usually printed in italics, with the rest treated as assimilated into English.
Latin: ad hoc (for a particular purpose, like a committee to plan an anniversary celebration), annus horribilis (awful year, as used by Queen Elizabeth II); bona fide (genuine), carpe diem (seize the day), caveat emptor (buyer beware), CV (curriculum vitae, career summary), mea culpa (I am to blame), pro bono or pro bono publico (for the public good, as when a lawyer helps a charity without charge), tempus fugit (time flies).

French: à la mode (fashionable), au fait [with] (fully informed about something), au revoir (goodbye), badinage (banter), beau monde (fashionable society), décolletage (low-cut neckline on women’s clothing), double entendre (something which can be interpreted in two ways, one of them dirty), femme fatale (seductive woman with a bad effect on men), né, née (male and female respectively, born, as put on forms for a woman’s maiden name), protégé (protégée if female; a person helped by a patron); raison d’être (reason for living); recherché (refined, known only to connoisseurs); risqué (almost indecent); R.S.V.P. (répondez s’il vous plaît, please reply).
German: There are assimilated war-related terms which are not given an initial capital letter, including flak (an acronym for anti-aircraft fire) and blitzkrieg (lightning war). U-boat retains its capital letter, as do Sturm und Drang (Storm and Stress). Other words keeping the capital letter include Doppelgänger (double in the sense of a look-alike), Übermensch (superman) and Zeitgeist (spirit of the age). Musical terms include Lieder (songs).
Greek: hoi polloi (the common people)

Never address someone by their first name unless you have established a personal relationship, even if only by letter or phone.

Try to phrase your message in a positive way rather than a negative one

Many of the phrases are clichés (see here) that we use unthinkingly:
• ‘further to the above’
• ‘the aforementioned’
• ‘at this moment in time’
• ‘at the end of the day’
• ‘in the not too distant future’

Do not explain an acronym if it is common, such as AIDS. If it is unusual or one you have coined, then explain it the first time that you use it in a piece, giving all the words in full. If an expression is used only once in your piece, there may be no need for an acronym when you can give the full words.

Use who for humans, which for everything else, whether living or not.

In restrictive clauses, that is preferred, but which is often considered acceptable as well