TW used to enclose "dress code requirements" with all Travel Agent award and discount tickets they issued.

For gentlemen in First or Business a coat and tie were mandatory. If a travel agent with a confirmed or space available agency discount fare ticket was not dressed in accordance with the guidelines, the gate agent could downgrade or even deny boarding. But I don't know of any cases where that occured.

But, like TW itself, I figured a dress codes for paying passengers is a thing of the past. And business casual should not attract any attention. The agent must have been having a bad day.