The time to tell me that you "are now vegan" was when you accepted the invitation for dinner, in which I asked you for any dietary preferences.
Or shortly thereafter.
Not a few minutes before I start to serve, making me rush around to turn out a vegan main course with zero planning.
*Of course* I will cater for you - I'd love to! - but that was an unwelcome last minute twist.
(Toot scheduled / sent from the past!)