Funny you should ask.
Story goes that I take a few classes here and there trying to better myself. I have a class that the instructor was PIC er. Captain of a 737 operator. His email correspondence with me has the title Captain. I was commenting on it when my wife chimed in on my conversation with myself. So I thought I would toss flightinfo.com a softball to see what everyone else thought.
Guess I am not the only one that thinks this is an improper use of a title. I have too many hobbies, right now I am making a peltier fan to sit on top of my woodstove so I can steal free electricity from physics. Google that!
Here's another opinion:
This is one of those gray areas, in that it's hard to articulate, but you'll "know it when you see it" (when the title is and is not appropriate, that is). Flight crew hierarchy, and society in general, has become more relaxed over the years, and with it, the use of such titles.
However, it was quite obvious to me that to actually ask such a question on a annonymous forum such as Flight Info, could only have one outcome: annonymous ridicule. This came to mind as soon as I read your original question, and it didn't take long to come to fruition. You likened it to "tossing a softball," but instead of hitting it out of the park, the batters simply caught it, and then threw it back at your head as hard as they could.
Bubba