OBVIOUS reason #1: Why do guys want RAINBOWS on their... well on any body part for that matter. Rainbows are connected with being gay. So why a straight guy would want a rainbow colored dick is beyond me.
OBVIOUS reason #2: Does it not disturb any of you guys out there that the girl who is putting her "mark" on you just had her mouth on another's guy's dick? Imagine this: precum from another guy being transferred onto your dick from this girl's mouth.
OBVIOUS reason #3: Wouldn't you much rather a girl give you a full on blowjob than to give you her "mark"?
Parent: whats a rainbow party?
Oprah: something i made up to get your children in trouble for absolutly no reason..
Parent: That sounds pretty mean but since your like a god and all i have to listen to you.
Oprah: i want to eat your babies.
At the second party, I was more relaxed, and before the end of the night had let each girl leave her mark.