Definition from Wiktionary, the free dictionary
probably from the similarity of the face to minced meat, Hack(fleisch), combined with Fresse, a derisive term for "mouth".
Hackfresse f (genitive Hackfresse, plural Hackfressen)
- (vulgar) very derisive term for a person that is perceived as ugly, comparable to shitface
- schau dir mal die Hackfresse an