devil's advocate
noun [ C usually singular ] uk/ˌdev.əlz ˈæd.və.kət/ us/ˌdev.əlz ˈæd.və.kət/
假意反对的人，故意唱反调的人
someone who pretends, in an argument or discussion, to be against an idea or plan that a lot of people support, in order to make people discuss and consider it in more detail
I don't really believe all that - I was just playing devil's advocate. 我并不完全相信那些——我只是故意唱反调而已。