A gloriously important tool for creating well-constructed sentences, grammar will nonetheless be made obsolete by 2011 when we make the transition to a language based solely on text abbreviations. Srsly.
First of all, in real life nobody ever speaks using correct grammar. Correct grammar is only useful in situations where you need to look professional or intelligent, i.e. at work, in an essay, if you're using words in an advertisement, etc. Good grammar can be a good thing if your words will be seen by a lot of people, because people are judgemental bastards and will tear you down for anything they can, so you might as well not paint the "bad-grammar bullseye" on your back.
Most of the time, in real life, this doesn't matter much. Though sometimes you will see something printed on paper (or a Cracked article) that contains spelling and grammar that is so incredibly bad, that you truly, honestly cannot understand what the fuck it is about. This is where bad grammar causes problems. If the only barrier between you and your audience is your... let's call it "gangsta"... grasp of language, then you might as well fix that bad boy.
Knows how to construct a question, but that probably still won't get him "all the chicks."
First of all, know your apostrophes. The apostrophe goes wherever something's missing, as in the word don't. Don't is short for "do not", so the apostrophe goes where the "o" should be in "not." It's the same with "didn't", "wouldn't", "can't", etcetera.
Another good thing to know is the difference between "their," "there," and "they're." Here are some examples of correct usage:
"There goes your filthy whoremaster of a mother!"
"Their mother is such a filthy whoremaster."
"Actually, they're all just a bunch of filthy whoremasters."
"So it's like my dick is the apostrophe, and your orifices are the missing letters!"
The apostrophe rule is also helpful when dealing with two things that sound the same, such as "your" and "you're." The second one is short for "you are," so the apostrophe goes in place of the "a." Example:
"Your intelligence is pretty lacking, so you probably have terrible grammar."
"You're a complete fucktard."
Another bad move: saying something like "I wouldn't of seen Transformers 2 if I were you..." when it should be "I wouldn't have seen Transformers 2 if I were you." Think about what it would be like if spoken out loud. You may be too lazy to clearly pronounce the word "have" in that sentence, but that doesn't mean you are actually changing the word to "of." Finally, learn the differences between words that sound the same, as in:
"This pair of slacks is stained with poo... I shouldn't have eaten that pear."
"I can't bear to look at your bare ass."
"This cock tastes like caulk."
Sometimes things get Tilda Swinton (read: really ugly) when someone uses bad grammar on the internet. A comment section will be rolling along nicey when all of a sudden, like an unholy storm of locusts, some dickhole with grammar issues will unleash a tirade about how uneducated every commenter is, and how the English language is going down the tubes. I just saw a site (not even kidding) that exists only to inform people of the correct spelling of the word "ridiculous," which I think is pretty god damn rediculous.
The fellow in the lab coat was sent an email containing the statement "Your so sensitive about grammar!"
Occasionally, you'll even catch a shitstorm of comments directed at one of these Grammar Nazis, like this totally-not-overreacting-to-something-trivial-at-all gem, found in the comments of a Cracked article:
What can I say... the Grammar Wars can get pretty rediculous.