Flat as a board （ぺちゃぱい）

He Says:
pecha pai (pronounced "pie") （ぺちゃぱい）=flat chested
What kind of pie do you imagine "pecha pie"?
New delicous pie?No!umm,but sometimes yes.
Pecha pie is flat boob.
So like a men breast, girls who have flat boob, we would call that pecha pie.
It's a little bit hard to explain why we say so. I think a pie is usually big because it has many cream or fruits inside. But when the pie is crushed or fallen, it can be flat. Pecha is an onomatopoeia word--the sound something makes when being crushed or made flat. So pecha pie is like no volume pie, it's a flat boob.
Many American guys seem to like Japanese girls. But Jp girls have usually pecha pie. It's hard to find a big boobed Jp girl.because the average of jp girls bust is said 82cm (about 32 inches).

She Says:
His description sums it up.
Japanese uses a lot of onomatopoeia words which are incredibly difficult for foreigners to master. You'd think that you'd just make the sound that something makes...but you actually have to know how Japanese people will say it. For example, to American ears the onomatopoeia words "kachung" and "darung" might pretty much sound the same. But to a Japanese person, they are totally different.
I'd always use the wrong onomatopoeia word and have people stare at me like I'm crazy.

The next word is...ポリコウ。

Hey Sexy Mama! （ちゃん ね）

He Says:
chan ne　（ちゃん　ね） = pretty girl.
Usually nechan is girl. It's a normal word. But if the word "nechan" gets reverse,it turns to have a little bit sexy. So jp men sometimes say chan ne~ to sexy girls or hookers instead of simply nechan. But we don't say chan ni~ to boys(nichan is boys or brother).

She Says:
Something you might hear walking down the street, the way that guys in English might call "Hey sexy mama" or whatever. If you're a foreign girl in Japan, guys might be more apt to say this loudly in front of you, thinking that you won't understand. So remember it and scare the shit out of them when you comment back. Really. It's fun.

The next word is...ぺちゃぱい。

That Toilet Training Video...

She Says:
I think that most people have probably seen the following toilet training video. The person who translated it did a very good job of getting the nuances right, but I thought I'd note a few things that aren't mentioned that are kind of cute...

• Shimajiro says byebye to "oshiko-kun" and "unchi-kun". "Kun" is a word that you attach to the end of little boys' names. ("Chan" is attached to little girls' names.) Since the word "san" gets translated as Mister/Ms when attached to an adult's name, I believe that an appropriate translation of "kun" would be like saying "Little Mr. ________" (Of course "kun" is also used between people of equal status in which case this translation is inaccurate.) So basically, Shimajiro is saying "Byebye Little Mr. Poo". Which cracks me up.
  
• The other day we talked about the word kimoi as a shortened form of "kimochii warui". At the end of this video, you can hear Shimajiro say, "Pants ga kimochii ii ne." He's literally saying "Underpants have a good feeling." It's translated as being comfortable which is a good translation, but I wanted you to listen for the word you know.
  
• Also note that the Japanese word for underwear is "pants".