So a little more about our Spanish T-shirt and onesie B de Burro, V de Vaca. Some people get it, immediately. But for those who may not have heard the saying, here's a little background on this Spanish saying.
In a former incarnation right out of college, I was a high school Spanish teacher, and one of the common mistakes that I saw amongst my native Spanish speaker kiddos was their confusion between the letter B and V. I'd often see words like "haver" instead of "haber" or "travajar" instead of "trabajar" or "escrivir" instead of "escribir." So why are the B's and V's so hard to nail down for those of us who grew up speaking Spanish? Here's an explanation:
B and V are pronounced exactly the same. In fact, one of the few spelling problems that many Spanish speakers have is with these two letters, because they don't distinguish them at all from their sound. Generally, the b and v are pronounced like the "b" in "beach." When either of the letters is between two vowels, the sound is formed kind of like the English "v," except that the sound is made by touching the lips together instead of the upper teeth and lower lip.
And I am the last person to be teaching phonetics, as I remember sitting in a college class and not being able to distinguish sounds. My ears apparently cannot fine tune. But here's more on that. And more.
So this is why when we have to deletrear something that has these two letters, we'll differentiate between B and V by referring to them as beh grande or uve or ve chiquito. Or you can make it more fun and just say B de Burro or V de Vaca.