I 've been using 
Pinterest for as long as I can remember, and I love it.  Not only do I post many resources and teaching ideas there, but I learn so-o-o much.  For example, I learned how to pack one suitcase with enough stuff for a week.  (My husband is thrilled with this one.)  I also learned that when you fry bacon, to make a small cup out of aluminum foil; pour the bacon grease into it; let the grease harden; then close up the aluminum cup and toss it into the trash.  That is one I use all of the time! 
 On my 
Pinterest account I have a board entitled Humor - We Need It!  I post many math cartoons or humorous sayings there.  My favorite subject to teach my college remedial math students is geometry, and I have plenty of corny jokes that I intersperse into my lessons.  Here's one.
What did the little acorn say when it grew up?  Gee- I'm - A - Tree!  (Geometry)
 
Or about this one?
   
What did the Pirate say when his parrot flew away?  Polly-Gone  (Polygon)
Here are some other geometry funnies from Pinterest.
Try placing a riddle or cartoon in the middle of a test.  I often do, and I know exactly where the students are by their laughs.  It helps them to relax and maybe get rid of those mathphobic tendencies.  I hope these math cartoons brought a smile to your face.  Have a great week of teaching!
You might also like 
Geometry Parodies, a four page handout that includes 20 unusual definitions of geometry terms.  Each definition is a play on words or a parody.  Twenty-six geometric terms that are possible answers are listed in a word bank, but not all of the words are used in the matching exercise.  An answer key is included.