I think this is a fantastic tongue-in-cheek commentary. We all loved our coaches, but at least a few did fall into stereotypes like our friend you pictured above.
My one suggestion is to do something to emphasize the whistle-ness. It almost looks like a pipe or something.
I really like him! If I had one thing I would change I think it would be his hands. Small hands and feet adds a funny contrast for this chubby guy, but I think his hands (or maybe it is his narrow wrists) are looking a little to feminine for me.
What a great character! As usual. :) I can really see his character in his face, expression, and some in his gesture, but I wish there was as much character in his figure as in his face. He's pretty flat and angular for a big guy. Not to say big guys can't be muscular, but his body seems over simplified. I say that because his figure is really where the pay off for your concept is and right now it's not participating in the story telling as much as it could be. Also, where you've created such great dimension in his face, his body disconnects a bit too much for me to feel like they belong to the same character. I also agree about doing a little more to describe the whistle as a whistle. Maybe a side plane and/or a string around the coaches neck. It's so great to see you're work. I'm really due to post on my blog too. It's coming soon, I just have to sit down and get it up. :)