If you want to disable WordPress smilies, the relevant function is in wp-includes/formatting.php. It’s called convert_smilies.
The smilies were annoying me. So I just commented out most of the function.
If you want to do this, just leave $output = $text; and return $output; and you’ll be fine.
Update: Never mind, the option is in the WP admin! Somehow I had managed to miss it, but Shelby pointed me in the right direction.
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