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.