A "Yellowtard" is an extremely fanatic supporter of the Partido Liberal (Liberal Party), a corrupt, Left-leaning political party in the Philippines. Yellowtard is a combination of the words "yellow" (Partido Liberal's party color) & "tard" (Retard)
Why do you keep voting for that Partido Liberal candidate? Can't you see she has a history of corruption? You're such a Yellowtard
when you're holding up your phone and making faces at it, as though you are taking a selfie, but you're really taking a picture of the person across from you or the wall or anything else that seems interesting but you don't want to be caught dead taking a picture of.
This action is often made more convincing by wiggling the eyebrows or opening the mouth, to pretend you're trying to get a Snapchat filter to work.