The O-Face originated from an emoticon which looked like this: o_O
It is becoming a fad/meme in YouTube Poop as people have begun to take note of faces on characters that greatly resemble the O-Face.
Thomas’ O-Face is commonly used in Thomas the Tank Engine Youtube Poops. It is gaining increasing popularity as more Thomas Poops are being made.
It is from the first season episode “Thomas Goes Fishing” of Thomas the Tank Engine and Friends where an inspector asks the fat controller what he can see in Thomas’ boiler. The Fat Controller after looking in the boiler says “Inspector? Can you see… FISH?!”. Thomas is shocked at this and you see Thomas showing a strange face with an, almost creepy, note playing as he pulls the strange face.
Many poopers have used this meme, mostly KeeperOfBeans.