With tensed muscles and looking "difficult" (as I don't know how to describe this any better...) Not done most excessively (a face frown as much as possible), but kind of like someone who (pretended or not) is having a hard time. You may have seen this kind of face before from young people who take a lot of "selfies".
I suggest hatchet-faced. It is used as the opposite of smiling,
I thus became both hatchet-faced inspector and smiling, helpful adviser who encouraged rather than drove.
-Admiral Sandy Woodward, One Hundred Days (2003)
- Hank Patterson was an actor in television programs Gunsmoke and Green Acres. He had a hatchet-faced expression in some, but not all roles.
- Jodi Arias was described as having a hatchet-faced expression in court.
Fleer To make a wry face in contempt, or to grin in scorn; to deride; to sneer; to mock; to gibe.
Gurning: intoxicated by drugs or drink. The term was popular among adolescents and students from the later 1990s and refers particularly to someone feeling the ill effects of drugs. It is inspired by the verb to 'gurn' (from Middle English girn, a form of 'grin'), which means to pull grotesque faces.
Pretty Girls, Ugly Faces:Pretty Girls, Ugly Faces is a photo fad in which girls take pictures of themselves while posing in an unflattering manner, making a silly face or performing a physically strenuous activity. Origin
The single topic Tumblr blog Pretty Girls Making Ugly Faces1 launched on September 26th, 2011, featuring nine photos of different females making unattractive-looking faces by manipulating their mouths and necks. Throughout 2011, the blog was regularly updated with the bloggers’ own photos as well as user-submitted images before going on a hiatus in June 2012.
Duckface: also known as “Myspace Face”, is a pejorative term for a facial expression made by pressing one’s lips together into the shape of a duck’s bill. It is often associated with selfies of teenage girls posted on social networking sites like Myspace and Facebook.
Girning: 1. to snarl 2. to grimace; pull grotesque faces