It's a metaphorical way of saying force sb. to accepet sth. usually ideas or beliefs,in English it's brainwash. 被反复洗脑:be brainwashed over and over Hope this helps.

in english, it's called 'brain washed'....so it means you are completly into a way of thinking or a certain value or moral system so that you can't accept other types of ideas which are different from you.

it's means someone want change your mind and make you agree with them ,so u join in them

it means that the idea of others instead of yours in your mind but you think it's nature.

Aaa：We must study hard.The responsibility for building socialism falls on our shoulders. Bbb：You are brainwashed.you must be a member of the Communist Party. (I think: empty all the information in your brain,and refill the thought of sb who wanna control you.) (if you know the situation of china,you will know the meaning of the talk )