put two and two together and make five idiom informal humorous
听风就是雨
to understand a particular situation wrongly, often in a way that is more shocking or exciting than the truth
"Why in the world did she think you were pregnant?" "I was sick a couple of times, and I guess she just put two and two together and made five." “她究竟为什么会认为你怀孕了？”“我曾呕吐过一两次，我猜她就这样想了。”