What does "say it straight or you'll show it crooked" mean?

In essence, it means that if I have a strong feeling or a desire, and I don't do something effective about it, I will end up, internally or externally, somehow demonstrating that feeling or desire in an ineffective manner.

For example, if I'm angry with someone, and I don't tell him that I'm irritated and what I'm irritated about, it's likely that I will consciously or subconsciously express my anger in another way. I may forget to do what he wanted me to do, do it wrong, procrastinate, do it late, talk about him behind his back, "accidentally" do him harm, take my anger out on somebody else, overeat, smoke, get depressed, worry, become agitated, or have sleepless nights.

That's the nature of the beast. Unexpressed negative feelings and unfulfilled desires get acted out in ways that are inappropriate if we don't express or act on them in ways that are appropriate.

"Say it straight" does not always have to involve sharing your feelings, thoughts, and desires with someone else, especially when the other person will react negatively to you for doing so, or is clearly unwilling to respond as you would like, or is not available to communicate with you. It is necessary, however, to admit your feelings to yourself, experience them, and utilize, in some positive way, the energy that those feelings generate for you.

You can use the energy to resolve your feelings in a variety of ways. You may re-examine the situation, and gain a new understanding that would help you to solve the problem, or you may become content to simply drop your anger, fear, or sadness. You may find some substitute way of getting what you want, or you may look elsewhere. Saying it straight means being sensitively, rather than blatantly, honest.