"I was on my way in, but I had to rescue a baby from a burning house, and I got burning baby all over my uniform, so I went home to get changed, but it's wash day, so I didn't have another clean uniform, and I know I can't come in without the correct uniform on, so by the time I washed and dried and ironed another uniform, it was quitting time anyway, so I didn't bother coming in."
Or....."I got really bent last night, then I got really hungry in the middle of the night, so I went through the cupboard in the dark and ate a whole box of laxettes, 'cause it was dark and I couldn't see, so now have explosive diarrhoea, but I haven't got any imodium, and it's so bad that I can't get to the chemist and home again without ****ting myself, and I know this because I've tried 5 times already, so I don't have any clean uniforms left, and I know I can't come in without the correct uniform......."
You just have to be imaginative