This is what you say when you want someone to tell you negative information honestly, without trying to be polite or concerned about your feelings:
Give it to me straight, doc. Am I dying?
What did you think of my performance? Give it to me straight.
You can say this about yourself also, when you have to give someone bad news:
Listen, Lee: I'll give it to you straight. I don't think you have what it takes to make the Olympic team.