Gary Oak (Also known as Gary Motherfucking Oak, or just GMO, which nobody ever uses.) is a common method of trolling and/or derailing threads using a popular character from the pokemon series, whose main character (ash ketchum) most famous rival (and still is). One specific Ponychan user, Keldeo, used them very frequently, and Gary derails were often met with a Spiderman counter-derail, thus further derailing the thread. These often became such a nuisance that Ponychan moderators would be forced to step in.
Gary derails became very infrequent around June 2011 since Keldeo received a permanent ban from Ponychan for unrelated reasons, but he has since been unbanned, he also likes to make threads which love to visit /chat/, /oat/ and a few other boards.