Depends on how old you are.
Old guys fart all the time and no one dares mention it :)

Because we all know they cant help it.
and we'll be old someday....

cannot help you with unwritten rules of urinal use. I have only been in a men's restroom a handful of times.. and never yet used a urinal.
I can say, though, that I believe it to be true that women feel no such need to apologize for that behavior... when in a stall.
Urinal is an entirely different sort of interaction though... isn't it?

related question: would you think it appropriate to apologize for farting in a group shower room?
what a topic for today......

Belinda says you're weird. :)