My favourite word is ‘muffled’, my favourite idiom ‘as cool as a cucumber’ and I don’t have a favourite tense in English, although I do in French. Or at least I did, until I found out that the subjunctive is a mood and not a tense.
Perhaps one of the more interesting features of English, and one which seems to be much more prevalent than in most other languages, is the existence of portmanteaus.
Do your students ever speak Spanglish? Do you know any Shopaholics? Chocoholics? Workaholics? What’s your perfect brunch? Ever stayed in a motel? Seen a Bollywood film? All portmanteaus.