Males SHOULD NOT be modest when it comes to other males seeing part, or all of their body. This is tied to body shame - a learned behavior - that can and should be unlearned. Guys, get over it already - the human male body is a masterpiece of design and function and we all come in different sizes, shapes and colors.. Celebrate the fact that you are a specimen of nature and don't let anyone tell you otherwise.
Me personally, I just step up to the urinal, whip it out and do my business. If others want a peek, then so be it. I refuse to hide in shame or feign modesty in the men's room just because another male saw my junk!