uśmiechać się złośliwie in English:

What are you smirking at?

She had a self-satisfied smirk on her face.

The boy smirked as he boasted to his friends what he had just seen through his neighbour’s window.

Stop smirking in such an unpleasant way.

Those teenage girls do nothing but smirk when they see boys they like

We smirk because we believe that...