The Tuchuks are a loose subculture in the SCA. Primarily a North American phenomenon, Tuchuks are barbarian personas who owe considerably more to popular depictions of barbarians in 20th century media than to the reality of barbarian cultures.
Bluntly put, Tuchucks dress like Conan and talk like Klingons. Leather, furs and maille are the norm, with lots of bare skin. The entire Tuchuk subculture is very medjeeval, and many SCAdians therefore look down on them for their lack of authenticity.
In defense of the Tuchuks, they throw excellent parties (especially at Pennsic) and they are pure hell on the battlefield. The chant of "Tu-Chuk! Tu-Chuck! Tu-Chuck!" is warning to get out of the way before they charge, since Tuchuks are content to mow down any allied unit in their line of advance.
Tuchuks should not be confused with the Dark Horde, although there is some crossover.