Sloppy handwriting and a not-100%-progressive coding style is my bane when it comes to whiteboard coding. For the last two senior level dev jobs I've gotten, I just brought a laptop with Visual Studio set up and told the interviewer I sucked at whiteboard coding and could I please do it in an IDE.
That’s definitely something I feel like I should try. I have failed interviews despite having optimal solutions because the way I went about it seemed haphazard (I was thinking in terms of 2 or 3 things at once and bouncing around).