Whenever I see a prospective startup founder with no product and no customers calling themselves a 'CEO', it triggers a little warning sign in my brain that this person may be too self-important to work with.

There are definitely times when you need the title to make meetings happen, so it's not a sure-fire guarantee of arrogance. But it's still a warning sign.

At the last startup I founded, both myself and my co-founder agreed to skip titles until such time as they were required. When pressed, we were both just 'founders'.