neprofesionalno

1. (of conduct, quality of work) unprofessionally
   Službenik se ponašao krajnje neprofesionalno. — The clerk behaved extremely unprofessionally.
   To je baš neprofesionalno od tebe. — That's really unprofessional of you.
2. (not as a profession) non-professionally; as an amateur
   Fotografijom se bavi neprofesionalno, iz hobija. — He does photography non-professionally, as a hobby.

Often used predicatively: "to je neprofesionalno" – "that's unprofessional".