Either way, really.
Do you really check out the guy next to you at the urinal? I certainly don't. I pee, zip up, wash my hands and move out. If it's at a sporting event and I happen to notice the other guy wearing an opposing team's shirt or something, I might say something like, "You're kicking our ass good today" or "boy are your guys sucking today".
Normally that's met with the appropriate response like "yeah, your boys didn't come to play today" or "yeah, we're toting an ass whooping today".
But hell, we don't sit there looking at each others penises and commenting on it. Who does that? Honestly?