I can contribute to this as i lived a couple of years in shanghai and now hong kong.
i've got a big cock and showing a bulge is natural, like having big boobs for women: therefore i did, an i do nothing to hide it
in shanghai i used to go to a very 'local' gym where i was the only foreigner and i can tell you i was pretty much the biggest in the locker room, got lot of staring but nobody ever commented. chinese in general are pretty reserved if they don't know you.
only once i got literally groped by badly drunk girl in a bar, kinda slut looking for white man i guess, and she said something like "what they say then it's true...", there is quite a few of these girls in shanghai, and it's fun at the beginning for lots of no strings sex, but later it becomes little bit dull...
i guess i am a serious guy
i'm goin little bit off topic, anyways show a bulge in china but in general don't expect any reaction, or if any it's from the kind of people i wouldn't spend a lot of my time with....
but if u are young do have fun as i did, having a big one is a plus here