Not one big enough to cause another great extinction, but small enough to just turn a whole small country and parts of neighboring ones into a huge crater. Will the people who was evacuated out after NASA stated a warning try to rebuild the country after everything has settled down or do they’d become citizens of another country?
Edit: after reading the comments, maybe turning a small country into a crater is too much, what about just level the place, or in any way that make it uninhabitable for a period of time?
if you like fiction Niven and Pournelle wrote a book in the 70’s called Lucifer’s Hammer that is about a big comet that breaks up and smashes into earth. The book is about the human survivors on earth and what assholes they all turn into, basically. Not exactly your scenario but it’s an in depth exploration of a similar concept. I’ll warn you it’s from the 70’s so there’s some racism and misandry and such in the book but it’s in interesting read for sure. It’s on annas archive.