In polish, calling people with the neutral gender. It's a grave insult which implies lack of agency and dehumanisation, and thank to some rightwinger assholes in parliament is also a specific transphobic insult now.
While in english it's completely normal thing to say if you're not sure of a person's gender.
So definitely not my "favourite", i would never said this to anyone in polish and i occasionally get a hiccup of misgendering someone in english because of that, but interesting from language point of view.