The Tuchuks are one of a number of independent organizations which participate at Pennsic War in the SCA. In fact, the Tuchuks had an event at Cooper's Lake before the SCA, and agreed to share the event early in the history of Pennsic. Primarily a North American phenomenon, Tuchuks are barbarian personas based on a series of books - the "Gore" (sp?) novels written in the 1970's - who owe considerably more to popular depictions of barbarians in 20th century media than to the reality of so-called "barbarian" cultures.
Bluntly put, Tuchuks 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 "Tooo-CHUCK! Tooo-CHUCK! Tooo-CHUCK!" is warning others to get out of the way before they charge, since Tuchuks are content to mow down any allied unit in their line of advance.