dark
angry
permanent
slight

wear
give (sb)
be set in
His face was set in a permanent scowl.

darken, deepen

in a scowl
Her brows drew together in a scowl.

with a scowl
He looked up at me with a scowl.

have a scowl on your face

angrily, darkly, deeply, fiercely
She scowled darkly and muttered something under her breath.

slightly

at
He scowled at her before stalking out of the room.