EVERYONE looks over at the urinal
I beg to differ. I have no desire to see what other guys are packing while they're trying to piss. Even if it was a woman, I'd let her go about her business without trying to get a peek.
In communal showers and such, I think most guys can't help but size each other up and compare ourselves - it is hardwired into out brains instinctively to want to be bigger and "better" than the next guy in every measurable way. Whether penis size is important right now or not, at some point during our evolution it must've been.
To answer the OP - No I don't mind a peek, but ogling and staring are rude (just like staring at a woman's boobs). I haven't found myself in a bathroom at the same time as any of my gay friends, so I can't answer from that perspective.
When I used to shower with guys that I knew were gay, I didn't have a problem with them getting a peek or an eyeful. Most guys just take a glance, some take a gander, some stare, and then even the most blatant offenders are done and move on to whatever they were originally doing. That's fine, as long as they don't try to strike up a conversation about it, or get pushy about trying to pick me up.
I had one (male) friend who was into holistic healing and was also really good at accupressure and trained in massage therapy. I saw him on a semi-professional basis - he'd do the accupressure and massage, and I'd pay him a small amount (much less than a licensed practitioner would get). I suspected that he might be bisexual, as I caught him stealing a glance down at my left thigh every once in a while - I found out later that he was gay. It didn't bother me then, and it doesn't bother me thinking back on it now. He knew I was straight, and never crossed that line from friend to "more" - and more importantly never violated the patient/healer dynamic.
At the end of the day, gay guys and straight guys all have the same equipment, we just aim it at different targets. No big deal.