Chirashi no Ura (チラシの裏), meaning the 'back of a flyer', is a Japanese term about how a flyer's blank backside is often used as 'scrap paper'. However, results may vary as fliers are not as durable, and businesses later realized that they can be less wasteful by making double-sided fliers.

In the past, some 2channel users would respond “write it on the back of a flyer” whenever a user starts to turn a thread into their personal blog, which says more about how easy it is to turn these 'anonymous discussion' zones into a chatroom when left unchecked. However, do note that people actually draw or write stuff down on the back of fliers too, so the context matters in some cases.

The text artwork borrows a scene from the one-shot gay manga, “My Teacher” (俺の先生, Ore no Sensei), by Gengoroh Tagame and published in Sabu in 1992. In the original scene, the teacher and student had admit their love for each other, so the teacher says “let's go lie down, ok?” (布団を敷こう、な！). It isn't known why this scene was chosen in particular, but one would assume that the context got lost.

　　　　　　r;ｧ'N;:::::::::::::,ｨ／　　　　　 >::::::::::ヽ
.　　　 　 〃　　ヽﾙ1'´　　　 　 　 ∠:::::::::::::::::i
　　 　 　 i′　　___,　-　,. = -一　 ￣ｌ:::::::::::::::ｌ
.　　　　　 ! , -＝=､´r'　　　　　　　 　 l::::::/,ﾆ.ヽ
　　　　　　ｌ　　　　　　　　_,, -‐''二ゝ　 ｌ::::l fﾞヽ |、 This isn't your diary,
　　　 　 　 ﾚー-- ､ヽヾﾆ-ｧ,ﾆ;＝、_　　 !:::l ） } ト
　　　　　　 ヾ¨'７"ry､｀ 　 ｰﾞ='ニ,,,｀　 　 }::ヽ(ノ 　write that on a back of a flyer or something,
:ｰゝヽ､ 　 　 !´ "￣ 'l,;;;;,,,.、　　　　　　　,i:::::::ﾐ
::::::::::::::::ヽ.-‐ ﾄ、　r'_{　　 __)｀ニゝ、　 ,,iﾘ::::::::ﾐ
::::::::::::::::::::Vi／l:::V'´;ｯ`ﾆ´ｰ-ｯ-,､:::::`"::::::::::::::;ﾞ　, 　ok?
:::::::::::::::::::::::::N. ﾞ､::::ヾ,.｀二ﾆ´∠,,.i::::::::::::::::::::/／／
:::::::::::::::::::::::::::::l　ヽ;:::::::::::::::::::::::::::::::::::::::::::／　／
::::::::::::::::::::::::::::::!　:|.＼;::::::::::::::::::::::::::::::／　／

• It can be abbreviated to 'ChiraUra' (チラ裏), but this is exclusive to anonymous communities.
• The aforementioned manga does have an English translation. It can be found on Page 30.

• Chirashi no Ura on the 2ch AA Illustration Project
• Chirashi no Ura on Pixiv Encyclopedia
• Chirashi no Ura on Niconico Encyclopedia