put two and two together and get/make five

to guess something wrong about a situation, usually something more exciting than the truth.

She thought I was pregnant. I was sick a couple of times and she just put two and two together and made five.

• someone's word is law
• someone will be along
• someone will go a long way
• someone won't bite
• someone would not be caught dead
• something and a half
• something be damned
• something can't hold a candle to someone else
• something can't hold a candle to something else
• something comes into head
• something comes into your head
• something else
• something falls on deaf ears
• something from hell
• something goes for
• something goes for someone else
• something goes for something else
• something goes to show
• something goes to show you
• something has more bark than bite
• something hits the fan
• something is all need
• something is all you need
• something is anyone's guess
• something is at disposal