I firmly believe that it is important that teachers express their vulnerability as much as their strength. As part of the SEL in my class, I post a laminated copy of the enclosed "Cranky Teacher Alert" poster any time I am overly tired (usually at report card time) or know I have a shorter-than-normal fuse because of life circumstances. It is one way I model self-awareness.
Be sure that the poster does not stay up more than a day or two at a time.
(For those wondering, B.I.C. stands for Butt In Chair. )
This is a free PDF version. If you want to easily customize the poster and/or use my grizzly photo for another personal use project or web page, a paid .doc version is also available.