This phrase is commonly used when someone is pulling a face that you would usuallyassociate with taking a poo (to strain) also often associated with a cum face.
Will you please stopgiving me the poo face, i know you're stressed - calm down!
Poo Faced girls who like to spend hours on the sunbed and end up having a face that resembles a large poo like structure, large "dow" like faces or fat chops are very common in the poo face race.
poo face: In reality this term is typically used as a random insult with little direct connection to the physical facial features of its' intended targets, it often is used in reference to someones unappreciated moods or actions. Although it my be used in refrerence to someones overall unpleasing physical facial features, but not in meaning their face actually looks life poo.
Your being a poo face.
Look at poo face over there.
Yah, he is a Mr. poo face.
OK there poo face.
Jeese, that girl has a poo face tough.