The "no NDA" thing is getting out of hand. NDA's have a time and a place. That place is not when you're meeting someone to talk for the first time. Nobody wants to increase their legal risk for a chance meeting, which will likely not turn into anything interesting - especially contract developers, investors, and the like (whose future business may be impacted by NDA's).

The answer is simple: state your idea in terms that don't require an NDA. When the conversation gets more interesting ad it's time to divulge the secret sauce, then ask for an NDA. If you've done this right, even the more NDA-averse among us will sign one. If you don't have secret sauce, you don't need an NDA - it's that simple.

What is secret sauce? If you can just think it up, it's not secret sauce. Secret sauce requires lots of tangible work. Innovative, tested algorithm: secret sauce. Financial resutls: secret sauce. Difficult to acquire dataset: secret sauce. Unbuilt concept: not secret sauce.

The concept to understand here is that when you ask someone to sign an NDA, you are asking them to give something to you. To make that work, you have to give them something in return - hopefully a high confidence that you're not wasting their time. Or money. Something.

That said, the surest red flag of them all is a premature NDA ask. In my experience it is literally a 100% indicator of someone who is not ready to be talking to people about their ideas.