R-espect L-evel D-own, an acronym which means that people will now respect you less. It is also similar to being owned or served because "railed" is what happens when you are shot with a rail gun in Quake. Rail guns are considered to own because they make for one-shot kills.
Person A: I love cuddly teddy bears and putting pink ribbons on my locker.
Person B: RLD!