A gurn or chuck is a distorted facial expression and a verb to describe the action. A typical gurn involves projecting the lower jaw as far forward and up as possible and covering the upper lip with the lower lip.

The English Dialect Dictionary, compiled by Joseph Wright, defines the word gurn as "to snarl as a dog; to look savage; to distort the countenance," while the Oxford English Dictionary suggests the derivation may originally be Scottish, related to "grin." In Northern Ireland, the verb "to gurn" means "to cry," and crying is often referred to as "gurnin'." Originally the Scottish dialectical usage refers to a person who is complaining. The term "gurn" may also refer to an involuntary facial muscular contortion experienced as a side-effect of MDMA consumption.