I haven't listed in 6 months so this is me just checking back in. Also you won't find like "l'espirit d'escalier" or anything particularly special. These are probably super mundane, but they're my favorites. This list is incomplete and subject to change.
  1. Donc
    It just means "therefore," but I (and many other English to French students I know) use it largely as a filler word, like "like" or "so"
  2. Dégoûtant
    "Disgusting." But I think the sound of it conveys the meaning of "disgusting" so so much better.
  3. Vous
    This is just the formal form of "you," but ever since I grew accustomed to using a formal "you," I long for one in English. Every single time I write a professional email, I wish I had a different, less familiar word to use than "you."
  4. Mon/ma petit(e)
    A term of endearment, meaning literally "my little." I just think it's sweet.
  5. Cou cou
    A cute way to say "hello."
  6. Merde
    "Shit," but far more satisfying
  7. Caca boudin
    Literally, "poop sausage." It's a mild expletive, and the most fun and gross literal translation of all time.