A really really silly looking animal or person. More commonly used towards animals. Less commonly used to describe people, unless their combination of facial features is really really really silly looking!
B: Awww what a cute cat, what's his name?
B: Yawnnniii to the McGeester face to the McGuyster face!
Person: dude, look at that guy.
Other person: omg, thats a McGeester Face if I've ever seen one!