Interesting topic. Guys that i know i dont mind changing in front of or getting naked for showering or whatever. We have a "penis warning" which means basically that you are changing your undies or getting naked to shower and please dont stare at the crotch. penis warning works by simply saying it, or saying penis or just being like " iam changing my dacks and i freeball so penis is coming out now" Its poor form to just change and have your cock out there without warning first.
Previous housmates i have been incredibly comfortable with, like i will just be in the shower whilst she is putting on makeup at the sink or going to the toilet and vice versa. I have all ways lived with girls and i am comfortable with being able to see them as just a person and to not stare or see them in a sexual way. I have seen most of my female friends naked, its not really a big deal.
In fact the most "uncomfortable" ive seen any of my female friends was one girl who was trying on dresses for me cause she didnt know what to wear and asked me to close my eyes in between dresses, didnt ask me to leave the room or turn my back or checked to see if i actually closed them or anything [ i did, i respect peoples privacy when they ask for it].
I guess when you know someone, or its your boyfriends mate or a housemate you get a lot more comfortable with them and dont really care if they see you naked