2. The act of a girl having her period in a guy's mouth and then making out with him.
3. A game played by girls where they put on different colored lipstick and make lines on the guy's penis in rings, it looks like a rainbow (note the name)
2. Last night when she was on her period, she rainbowed with him.
3. Last night those bitches rainbowed him and then afterwards his penis looked like it had gift wrap ribbons on it.