When you kneel on the floor, pants down, cock in hand, then lay out all your favourite porn mags on your preferred climax pages in a rainbow shape around you and then have a wank.
My Mum walked in on me having a rainbow wank last night! I couldn't hide the porn mags quick enough.
When 2 or more girls (preferably more), each with a different color of lipstick, compete to see who can get their lipstick the lowest down on your dick
"Dude! The other day Sarah and her friends gave me a Rainbow Road, Jessica came first with purple"