When you scowl you make an angry face. The angry face you make is also called a scowl. Lighten up.
Scowl is an expressive word: it shares "ow" with frown, and if you say it like you mean it you might end up scowling yourself. Being scowled at is more unsettling than being frowned at. A scowl is like an angry frown you would give someone if you disapproved of them. A frown expresses sadness, but a scowl expresses disdain.