In January 1980, Paul McCartney flew from New York City to Tokyo for an 11-night tour with his band Wings. He decided to take half a pound of marijuana with him because it was "too good to flush down the toilet," he explained to Uncut magazine in 2004. Upon his arrival, Japanese officials promptly found the illegal substance. The tour was canceled and McCartney spent 10 days in a Japanese prison before he was deported. "It was the daftest thing I've done in my entire life," he later said. Oh, we don't know about that. Surely writing "Silly Love Songs" must have been worse.
Bonus trivia: McCartney has actually been arrested for pot possession four times. It happened twice in 1972 and once in 1984.