Very true Ignition...
No FO should be intimidated, FO's should never hesitate to challenge, enquire or express concern.
Strong words like "I'm not happy", "I'm concerned" or even "I'm uncomfortable" should alert the captain to evaluate or re-think the moment/situation.
I know it is easier said than done especially with junior FO's when questioning actions or decisions by the captain, no human being is the same or perfect, we all have different reactions or attitudes to everything in life, but we can learn and adapt to ensure cockpit efficiency, safety and awareness.