His character just didn't have anything interesting to do.
Except he did. He had plenty of interesting things to do throughout the movie.
Plus if his focus in that movie was getting laid at least that'd make sense
No, it wouldn't make sense and it'd be a completely awful idea. It's been shown throughout the series that Jack's swagger is slightly misplaced, such as being slapped by the wenches, Elizabeth's indifference towards him, etc.
He just kinda wandered aimlessly and not as entertainingly as usual call me crazy.
Except he wasn't. Quite the opposite, he was being railroaded down a path he wasn't completely comfortable with. You can see his general uneasiness with the situation throughout, compared to previous movies where he goes the way he feels until someone gets wind of his little plan. It's a completely different approach to his character.
Think about it, the free wheeling Jack Sparrow now tethered to an undesirable path. He has no real chance to reason/trick his way out the situation.
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TheRock ~ Slow dramatic zoom-pan. Doesn't phase the hooded man.