Touchy subject, I guess, but somebody has to do it. A co-worker/manager (not my manager, just a manager although he's part owner) has several side businesses that are totally unrelated to the company that I work for. One of these is an SaaS application that he continually mentions to me in casual conversation; it's not anything revolutionary.
I'll get right to the point: I believe that I can do this idea better than he can, and I want to write my own similar application to "compete" with him. I see nothing wrong with this, as he has not asked me in any way, shape or form to do anything with this business, just blurted out what it is going to do and given me the URL of his website for it that has information regarding it.
Obviously I'm not going to steal his code or anything, but I do plan to take the concept of it, improve and make it my own, and then try to sell it. This is, after all, how business works.
I see nothing unethical about this, since I didn't ask him about it - he just likes to blurt it out to anyone within earshot about how great this new service is. What are your feelings on doing something like this, keeping in mind that I'm really taking the idea and changing it around; obviously some parts will be similar due to the type of application it is, but I'm not lifting his work.