Pronunciation
If someone mis-pronounces a word it is very rude to correct their pronunciation - they will feel crushed and foolish. The tactful option is to re-introduce the word that has been mispronounced into the conversation: by using the correct pronunciation you will be alerting them to the mistake; they can either choose to rectify their error in future, or stick doggedly to their own version.
While everyone admires linguistic ability, you should restrain any desire to show off your skills by over-pronouncing foreign words. Generally, if foreign words are used in English conversation they are gently anglicised; guttural or phlegmatic consonants, trilled 'rs' and exaggerated glottal stops are unnecessary and obtrusive.
