RRRrrrr!!! (2004)
RRRrrrr!!! is a 2004 French comedy film set in 35,000 BC. It features two tribes, the Clean Hairs and the Dirty Hairs, who have been battling for control of shampoo for 800 years. The Dirty Hairs tribe concocts a plan to steal the secret of shampoo, sending someone to infiltrate the enemy. When two members of the Clean Hair tribe are killed the chief instigates the first ever police investigation.
More at Wikipedia.