Everyone should have a sense of humor and no one should be off limits when it comes to mockery.
I go by only one rule, you gotta be funny! So by my standard;
mean (plus) funny = good
mean (plus) not funny = bad
I will give you an example. One of my favorite jokes goes like this;
"What do you get when you cross a sleazy politician with a crooked lawyer?"
Answer= Chelsea Clinton
As Larry the Cable Guy likes to say, that's funny I don't care who you are.
(never heard a similar joke with the Bush twins as the punchline that was anywhere near as funny, and there is nothing funny about Obama's kids, they are too little)
Edit note to the Ice Cream guys, the plus sign still doesn't work. 
calhob
I can't think of a fruit so ripe for the picking.