What is an antonym for smirk?

Here are some antonyms for smirk, depending on the context:

General:

* Frown

* Scowl

* Grimace

* Glower

* Sulk

More specific:

* Smile (genuine, open smile)

* Grin (wide, open smile)

* Laugh (expressing amusement)

* Wince (expressing pain or discomfort)

* Pout (expressing displeasure)

The best antonym will depend on the specific meaning you want to convey. For example, if you want to convey a feeling of sadness or displeasure, "frown" or "scowl" would be good choices. If you want to convey a feeling of genuine happiness, "smile" or "grin" would be better.