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To have a preference towards younger members of the opposite sex, preferably younger siblings of good friends.

"Oh My God. She's hooking up with my 15 year old brother. Trust her to Pull A Gwyther."

"My best friend pulled a Gwyther. I never knew she would go there."

"He was 7 years old and she was 18 years old. Pull A Gwyther much?"
by Geese April 03, 2008