Sure. Let's take a look at your sentence:
"You cant really mean that Obama is your hero."
As written you stating that I can't mean that Obama is my hero. Since I never said that, the sentence is true on the face of it. But what I think you meant was this:
"You cant really mean that. Obama is your hero."
Which is equally inaccurate but would indicate that you don't believe that my criticism of Obama is sincere and it would imply that Obama was a hero of mine. Nothing could be further from the truth. If Obama's been dipping his wick away from Michelle then my disapproval is the least of his worries, she'll probably cut his wee-wee off. And Obama isn't any hero of mine. Never has been.
Or it can be written as below.
You cant really mean that; Obama is your hero.
Or using a conjunction:
you cannot [can't] really mean that because Obama is your hero.
The sentence was short so there was no misunderstanding, and informal writing on forums are the norm.
And Obama isn't any hero of mine. Never has been.
I read your posts all the time... and you make excuses all the time for Obama.