How do people become a blunt person?

Just tell the truth.

Let's take a real example.
My husband reached a stage when he stank so bad that I couldn't bear to be in bed with him.
I said, "Honey, I have something really difficult that I need to say, and I'm afraid you won't want to hear it."
He took a huge sigh and said, "Okay, I'm prepared now. Tell me."
- "Well, you know how I've been sleeping on the couch for the last nine months and you keep wanting me to come back to bed?"
- "Yes."
- "It's because there's been a change in your smell. You smell like an old man in a nursing home."
- "I don't believe it!"
- "I'm sorry, sweetheart, but it's true. I think it might be something to do with a drop in testosterone, but I think the main thing is hygiene. And I don't think you can smell yourself because you're so used to it."
- "Well what can I do about it?"
- "I'd like you to wash your pillow slip once a week, shower before bed and wash your hair, only wear freshly washed tee-shirts, and wash your clothes once a week."
- "Okay. I'm willing to give it a try."
He kept his word the same day.
That night I returned to the bed, he's kept clean since then.
He's happier, and I'm getting much better sleep.

The problem is with blunt people they often don’t like it when you’re blunt back. Tact is required. We can tell the truth in a gentle way without using a sledgehammer to crack a walnut

The key is you gotta speak before you think