Short for "Rot Off." A rot off is a member of the female persuasion who, as a result of engaging in sexual intercourse with multiple partners (males, females, animals etc.), is a host to a number of venereal diseases. The R.O. will then procede to spread the diseases, resulting in her partner's genitals rotting off.
R.O.'s include but are not limited to:
Short for "Snap Off." An S.O. is a female, usually overweight and unattractive, who finds it difficult to find a male partner who will engage in sexual intercourse with her. When the S.O. finally "gets lucky", she will ride his genatalia so hard, it will snap off under the pressure.
"Oh man, you hooked up with a real ugly chick last night."
"I know had to ice my nuts because she was a real S.O."