What does this sentence mean?

Look at the image above, which is of a man wearing a shirt (what in the English speaking world is known as an oxford shirt). I chose this picture because it is shown from behind. At the bottom is the shirttail, that portion which, if this man were wearing a suit and tie, would be tucked into his pants--he would put on the shirt, and then pull on his pants (trousers) over the top of the shirttail.

So, the makers of Hathaway shirts are advertising that they make shirts with long shirttails, which will not come out of your trousers, and therefore embarrass you in a professional setting.



This image of Mr. Obama and some of his advisors shows them "in shirt sleeves," meaning that although they are still dressed in formal clothing, they have taken off their jackets. For men in the world of business or the professions, it would be embarrassing to be in shirt sleeves, as these gentlemen are, and to have one's shirttail come out of the trousers. Hathaway is saying that that won't happen to you if you buy their shirts.

(Hathaway does make a high quality oxford shirt, if they are still in business. I've bought their shirts in the past, and thought i got good value for money. I don't recall the shirttails being noticeably longer, though.)