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1.
Cunnilingus when the girl is on her rags(period). the aftermath is having period all over your mouth. creating a rainbow of colours and a terrific after taste.
you could'a told me your mum was on her rags last night, i went the growl and ended up with a rainbow pash
by callum thomson September 23, 2006
 
2.
Cunnilingus while the woman is on her period.
This is followed by an open mouth kiss which is ideally bloody.
Adam: I think i might be a vampire!
John: Why would you think that?
Adam: Jill requested I perform a rainbow pash on her last night and i quite enjoyed it.
Adam: Stop biting my neck!
by van_tango January 16, 2008