to have an affair with your best mates wife
"My best mate was sleeping with my wife...yeah he did a Garry Lyon on me"
A common phrase used in country victoria that refers to one getting fucking loose with their mates. Best used in past tense to truly describe a large and eventfull night out.
"Hey Morrey, what did you get up to on the weekend?
"Eddie! I was smokin cones & drinkin piss with garry lyon all weekend, was bloody elite"