Let me get this straight

A recent question on the Help Me! forum asked what this expression meant. As one person suggested, it can also sound quite aggressive, as in some situations, you are saying to the other person that you don't believe them.

Other phrases you can use to tell someone you don't believe their story are:
You're joking!
You've got to be joking!
Rubbish! (Also quite aggressive)
No way!
I just don't believe you!

You can also use the phrase "Let me get this straight!" when you are trying to understand two different points of view – perhaps from two people who are arguing. Perhaps their stories don't make sense or are contradictory, and you want to repeat the stories to make sure you understand.