pull a face = make a funny face He pulled a worried face at the issue.

I have a set of examples here for you: http://www.youtube.com/watch?v=N4Vf9QMROCQ&feature=related

If somebody does something awkward or unacceptable in a social situation, we can say it was a real facepuller, even though we didn't make a face. Another example is we could be having fun at a party and then somebody could drink a whole bottle of red chilli sauce and this would be a real face fuller as well, but because it wasn't awkward we would actually make faces. We have other sayings as well like 'It was a real jawdropper' to say that we saw something happen and we just stood there with our mouths open in disbelief. And we also use the expression to say something was unbelievable but we didn't actually stand there with our mouths open.

To "pull a face" means to make some kind of unusual facial expression, probably intended in response to some situation or emotion. Then the resulting noun would be a "face-puller", referring to the situation or emotion that caused the response.