A designated member of a group who is responsible for keeping the promiscuous individuals from doing something they will regret later. The slut butler is usually designated when the group is out at a bar or club while consuming alcohol. Only he/she is allowed to let the other members make the sexual mistakes that are inevitable.
"Who let the dirty slut out of the slut house?"
When a slutty friend wants to go hit on a guy and has to get the nod from the slut butler that she is allowed to continue in her pursuit of unholy activities with a stranger.
Some guy was hitting on me at the bar last night, but our slut butler wouldn't let him anywhere near me.