Charlie Sheen -- Kingpin in Colombia

Charlie Sheen is vacationing in Colombia -- and for the first time ever, the locals are worried they could run out of cocaine.

Just kidding ... but the Warlock is in the country with some kind of film crew -- and yesterday he was seen strolling around Cartagena ... even visiting a local library.

According to local reports, Sheen was very friendly ... and posed for pictures with fans.

As for the film crew -- it's unclear if The Warlock's shooting a documentary ... or if he just enjoys having people follow him around with cameras.