you could cut the atmosphere with a knife1 informal used to say that everyone in a place is very annoyed or angry with each other and this is very easy to notice 气氛很紧张 → you could cut the atmosphere with a knife at cut1(27)
2 used to say that you felt the people in a room were angry with each other 〔感觉到屋内的人相互间〕气氛很不友好,使人透不过气来 → you could cut the atmosphere/air/tension with a knife at knife1(5)