50 Cent was arrested in St. Kitts in the Caribbean Saturday night ... for using a word that's apparently illegal there ... 'motherf*****."
Sources tell TMZ, 50 had been warned not to use profanity during his performance in front of 40,000 people. We're told the DJ didn't have a clean version of his set, and 50 didn't pull the mic away from his mouth when he roared, "motherf*****" ... and that was enough to get him arrested.
Cops showed up after the performance and took 50 to the station, where he was booked for using profanity in public. It's a minor offense, but he has to stick around until Monday when he'll go to court and pay a fine.
The same thing happened to DMX in 2003.