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2.
When one has consumed a particularly dodgy curry or food dish, the results of which are for one to have a severly inflammed sphincter (hence 'jap flag'). There maybe some discomfort when passing faeces. Jap flag is often associated with sibling terms "turtle head (turtling)", "Ring-Stinger" and "touching cloth"
"That was a dodgy curry last night, I think I'm jap flagging"

"I am experiencing a case of Japanese flag"

"Excuse me your majesty, I must depart immediately, I'm touching cloth and being partiotic I hope I dont wave the jap flag"

"That ring stinger has left me with a severe case of Japanese flag"
by El Dinho September 22, 2006
 
1.
When a woman experiences her period in the middle of the night while sleeping on white sheets, leaving a giant red dot.
I gotta get new bed sheets, i woke up on the japanese flag this morning.
by TheOrcaWhale July 16, 2011
 
3.
When you have sex with a woman on her period and youre left with blood on the end of your penis. Then using a clean piece of toilet paper press your penis bang in the middle of it leaving a red circle.

Or if you have a large length, you could always use a bath towel and fly it from your TV aerial.
There's alsorts of japery to be had when "the reds are at home"

Best laugh you can have is doin the Japanese Flag with a bird who has "the painters" in.

Whip yer cock out after a few dips in the tin and place the end of your length slap bang in the middle of a clean piece of toilet roll.

HEY PRESTO!!!! 1 Japanese Flag.
by L4TW August 18, 2007
 
4.
Describes the effect of eating too much hot food, on the anus. White with a glowing red spot in the middle
Man that Vindaloo just reached the other end, burned so much I was jumping round the toilet rim, now I got an arse like a Japanese Flag
by Jules W December 08, 2008
 
5.
What you call your sheets after you rail a girl so hard she bleeds all over them.
I made that girl buy me new sheets after she turned mine into Japanese flags.
by Lil' Bandit January 12, 2008
 
6.
A bloody and used maxi pad.
I'm sick of seeing Japanese Flags in the trash can.
by LeeChan January 20, 2004
 
7.
Last night's Ruby Murray has got me sitting on a Japanese Flag today
by Slim_Jim October 22, 2008