Maybe the reason Julia was "wearing" the garter belt and stocking was be get Barnabas jealous.
You know how boys are....the next night at the Blue Whale...... Barnabas.... smiling Elliot..... of course Roger...and of course, Sam Evan. They're all smiling, as Elliot procedes to tell them about Julia and the grater belt. They're all drinking beer or brandy, laughing. I feel sorry for Julia. Her plan backfired.