It may actually be required by law in some jurisdictions that if you pin, you have a funny board.
Remember when many many people were new to the Internet? Every now and then someone in your life would go through that phase of passing along every single e-mail that came their way that made them giggle. Not to mention hoax virus warnings and the one about how Canada Post was going to start charging us a dime every time we had a naughty thought? And it wasn’t horrible. You like a good laugh as much as anyone else, right? But the four people you’d had to kindly dissuade before this particular mad mailer started hitting SEND had also forwarded all of these exact same silly things when they discovered them, six months and a year and two years and three years ago?
Now this niche has been filled by Tweeting and posting teh funnies to Facebook, and we can set our filters to pay a lot of attention, if we wish, or dial it down to none. I like Pinterest for this, for the simple reason that it keeps everything I find amusing in one easily clickable place.