Warning: Spoiler! (Click to show)
(edit: it was pointed out to me that I am wearing a baseball cap in this picture. It was in the hallway as I was walking in, and I tossed it on with the intention of putting it away. And then I got distracted. I would never wear a baseball cap with a tie or jacket or slacks of any sort. Promise)
I think Ralph Lauren has shown more than a few successful baseball cap, tie and jacket combos. As long as all the other elements are equally as casual as the hat, I don't see an issue with it.
Based on comments from this thread this week, I have two ideas for new Friday challenges: baseball hat challenge and the tie and no jacket challenge. I'm sure those would be serious challenges for many.