Related to "lasers" and "shoop da whoops", a "Royal Rainbow" is what happens when a taco is forced into the mouth of the person charging their laser. The caster instead releases a Royal rainbow, and possibly the swallowing of one's laser, and can end in the shooper asploding.
To throw up profusely, normally in the figurative sense. Usually in response to something that is too cute or just outrageous for words. Done in the fashion of the King of CosmosfromKatamari Damacy in which the person emits a large rainbow from the mouth that has pink instead of indigo for some reason.
My girlfriend is so cute, she makes me want to Royal Rainbow whenever I see her. It must be love.