I'm probably in the minority here, but I don't think everyone needs to go to a fitter to get his proper bra size. The most prominent reason is that it is impossible to determine their bra size, as it does not exist. The is no single bra size that is the correct bra size. Different brands use different methods for sizing bras. Some use band measurements, some band measurements plus 3 inches, some plus 4, some plus 5, and others use the measurement under your armpits to determine the band size. On cup size, some go off the band measurement, some go off the band size. Then even within brands, they seem to have different fits between different styles of bras. So if you find someone that is competent at fitting, they are not giving you your bra size, but rather a bra size or sizes that fit you for the bras that they sell. Now if you can't figure out your correct size for the models you try, then go to a fitter. If you find that the band size you select is 4 inches off what a fitter comes up with and find that their recommendation is comfortable, you should get help from a fitter. When someone says that he is a 48C or 48D, that does not mean he is ignorant and needs to go to a fitter, he may know the general sizes of bras that worked for him, and we can use that as an idea of what size he is.
From what I've read, it seems that the guys that have smaller cup sizes, A or B, they like sports bras. Some like the compression bras while some prefer the encapsulated bras for more comfort. They also tend to be shallow, so the breast fill the bottom of the bra, but not as much on the top, so molded cups and underwire bras have gaps on the top of the cups. The guys with D cups and above fill the cups (when sized appropriately), and find that underwire bras tend to be more comfortable for them.
One other word of advice, when determining your bra size, be sure to go to the manufacturer to get sizing recommendations. It is amazing to me how many retailers give links to bra sizing that does not match with the manufacturers. If you read the reviews, it is not uncommon to read reviews of people complaining that the band is too tight, but find that the manufacturers method is based off band plus four or five and the retailer goes off band measurement (plus zero). You'll also see many reviews are given across multiple retailers, often linked via Amazon, so some people complain that the bra band or cups run small, and other complain they run big, because the reviewers use different incorrect methods to determine their assumed bra size.