In some European countries, there are special laws for insulting the monarch. In others, there are laws for insulting foreign heads of state. These laws are sometimes enforced.
For example, two Spanish cartoonists were fined for depicting the Spanish king having sex with his wife captioned with the "unpopular opinion" that getting his wife pregnant was "the closest thing [the king has] done to work in [his] whole life": http://news.bbc.co.uk/2/hi/europe/7092866.stm
Interesting. I'm surprised that happened, thanks for pointing it out. I've been trying to find more information on the case (to see if the ruling was appealed) but I can't.
Thanks for spurring me into looking up more about it. As a correction, while the person depicted is in fact the present Spanish king (Felipe VI), following his father's abdication, he was at the time prince.
For example, two Spanish cartoonists were fined for depicting the Spanish king having sex with his wife captioned with the "unpopular opinion" that getting his wife pregnant was "the closest thing [the king has] done to work in [his] whole life": http://news.bbc.co.uk/2/hi/europe/7092866.stm