Satire is a genre of literature, and sometimes graphic and performing arts, in which vices, follies, abuses, and shortcomings are held up to ridicule, ideally with the intent of shaming individuals, and society itself, into improvement. Although satire is usually meant to be funny, its greater purpose is often constructive social criticism, using wit as a weapon and as a tool to draw attention to both particular and wider issues in society.
I share this today because people are increasingly using the words "satire" and "humor" interchangeably. But they're two different things.
A rodeo clown wearing an Obama mask is not an example of satire. It might pass as a joke if your sense of humor sucks, but it isn't satire. Satire skewers. A rodeo clown wearing a George W. Bush mask might be satire, because Bush had a reputation as a cowboy (and as a clown). But any supposed satirical subtext of Obama as a rodeo clown is like making fun of Ben Affleck for the holes in his hands.
(Wait. Scratch that. I can think of one way Obama as a rodeo clown is satirical. Rodeo clowns distract rowdy bulls. That's kind of what Obama's doing, isn't it? Brilliant! The clown is actually an Obama supporter! Who knew?)
To use another example, if someone satirized Sarah Palin for being overly pretentious, that would also be a fail. Not that I see anyone doing that.
Satire is best described as thinking person's comedy. So if you find yourself trying to hide behind the term, that's what you need to do before you speak. Think.