Called in sick with “food poisoning”.
I called in sick a few times as a teen, including making up a sickness, but the giving a reason and especially a fake reason just didn’t work for me, it made me feel servile, and the fibbing didn’t fit me at all, for the rest of my life I just told them that I would not be there today, no reasons, no excuses.
I'm having great success with telling them that every single day.