12. Sparrow's Sexy Scab
The welt on Jack Sparrow's chin was added as something of an in-joke between Johnny Depp and the make-up team. Throughout the first film it gets progressively more obvious, suggesting that Sparrow is infected with syphilis.
There are other character references that were ad-libbed: Orlando Bloom's riff on Depp's Sparrow performance in the first film was unplanned, and Depp himself suggested Sparrow should have gold teeth (and had his dentist implant more than the producers actually wanted).
And of course, the "Bring me that horizon" line in the first film was also ad-libbed - leading, unintentionally to the naming of British rock band, Bring Me The Horizon.