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When a chap is 'knocking one out' in his leisure time, lying on his back, preferably with someone watching from a distance, and blows a big load- quite high- that lands either in or around the mouth area. Making the shape of a low arching 'milk rainbow', result.

Derived from the ancient red indian word "milainbow" meaning to spunk on ones own face, or the face of a Yak, either by accident or on purpose. Such men in these tribes were worshipped for their big loads, and creative catching with the mouth abilities like a Jack Russell -thus commonly called "Jack-Russelling" in the gay community.
Andy-"Oh man last night I got spunk in my face!"

Peters-" Did it go in your mouth dude?"

Andy- "A little bit, why?"

Peters- "Mate, Milk Rainbow"
by "TheMurph" November 12, 2009
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