Matt: In Chinese, "nai3" 奶 functions the same way in that it doubles up in baby talk (though then it can be read in a "cuter" way, "nei3nei") and can mean breast or milk).

Oooh, I have something relevant for once! Kinda.
At Fed square the other day during the Aus-Jpn match, my pal Jimmy tried to impress a couple of Japanese girls with his mad language skillz: "Ahh, boku wa ookina oppai ga daisuki...demo, chisai oppai mo daisuki...boku wa nandemo daisuki!"
The girls seemed oddly impressed, so he continued on, telling them that he loved them and that he thought they oughta get married some day. The girls eventually ran away ofcourse, but not before repeated photos were taken and pledges of eternal friendship were made. How glorious multiculturalism is.

...and it really was my friend doing the talking...I just stood by and interjected with the odd "Maji de!" here and there...honest...

Kitto: Sports really do bring people together! I think your friend needs to listen to the "a cup, b cup, c cup, d cup" song and narrow it down a little, though.

Amida: So, assuming that nai3 worked the same way 1000-odd years ago (which seems reasonable), I guess that means that when it was borrowed into Japanese as a higher-status word it got more specific (technical, even?). That's interesting.

Is nei3 inherently cuter than nai3? (I can see why the repetition is cute, but I don't get the vowel thing)

p.s. that was me

I guess dipthongs are not cute.
When you say Chinese loanwords, do you mean compounds? How about 乳房 and 牛乳? Chichi can be written 乳, but you never can trust Japanese kanji.

Yeah, I guess I meant, I've only seen the word used with a Chinese reading in multi-syllable words, and there it always means one or the other. Maybe that's just because they are multi-syllable words, though... it can still be used with either meaning to make new words, now that I think of it (unless 爆乳 and 乳酸 were in ancient Chinese too.)