This one is not exaclty a Japanese word or phrase, but it's in Japanese, and it was amusing, so it goes here!
I found this while reading the popular Doraemon manga. At some point the main character wants to proove to some girl that he has a super memory so he goes over a phone book's first few pages and then asks her to test him. She names names of people and he recalls their phone numbers!
Obviously the author needed to throw out some random not important to the story names for this test. I imagine in English "John Doe" or "Jane Doe" could be used, though, not sure since it's not quite the normal use for those terms.
So what were the names that amused me so much and why?
Here you go!
Reading: aiueo san
Meaning: Mr. aiueo
Reading: kakikukeko san
Meaning: Mr. kakikukeko
What is amusing about that?
Well, if you studies Japanese even a little bit, you know that when learning Hiragana or Katakana, the syllables are written in a table in that order so you kind of get used to the aiueo, kakikukeko sound/rhythm. It's not quite like Mr. ABCD, it's something a bit different.
Plus, it's written in Kanji! And valid one at that! When I first read this, I knew it was a name because it ended with the hiragana "san" but I had to turn to the furigana to help me read it, and when I finally realized it's just aiueo/kakikukeko, it was just funny! lol
Funny because it's a totally bogus name, but it hides so well in the Kanji that it really looks like a real name! Unlike Mr. ABCD which is obviously fake from the first glance.
Another amusing thing is that we can probably guess that aiueo san is a man and kakikukeko san is a woman. I'll let you figure out why yourself!.
Did I mention I started liking Kanji? yeah.