おかえりんこ
This difficult-to-translate [[pun]] comes from stories of practical jokes long told on [[2channel]].

The archetype, as retold in post #116261:
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Upon her return home, I said to my little sister - an 8th-grader - "[i]Okaeri-nko[/i]."
("[i]Okaeri[/i]" means "welcome back".)

She started to respond "[i]Tadaima-nko[/i]", before suddenly turning bright red and hitting me, saying "Geez! You pervert!" I got a huge kick out of her innocent reaction.
("[i]Tadaima[/i]" means "I'm home", and "[i]manko[/i]" means "[[pussy|vagina]]".)

Later, when my older sister came home from work, I said "Okaeri-nko" to her, too. Without the slightest change in expression, she responded "Tadaima-nko. What's for dinner tonight?" Impressed, I couldn't think of a thing to say.
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This story was already in existence as of [[2003]]. As it has been spread around, various small variations have shown up.
It's particularly popular among boys with older sisters, and there are people who have actually tried it.
"[i]Okaeri-nko[/i]" is probably a variation on a the slang word "[i]tomodachi-nko[/i]", which is found in "Kobayashi Yoshinori":http://en.wikipedia.org/wiki/Yoshinori_Kobayashi 's manga "[i][[Obocchama-kun]][/i]."
("[i]Tomodachi[/i]" means "friend" and "[i]chinko[/i]" means "penis.")
okaerinko