A movment of the face and/or jaw whilst under the influence of ecstasy.
Many examples of this can be seen in nightclubs across the uk, a very rare case and example is someone who goes by the name of "brian" or "Gurn-tits" usually found in a night club called the krazyhouse. gurning on a an object to prevent his jaw from locking eg a shoulder of pork.
check out his gurn
does it look good when i gurn?
woah is he gurning on a leg of lamb?
15👍 74👎