Watch the Glass!

In other words, here are the grammar rules you do not break, even in dialogue.

• Spelling.
• Rules about good sentence structure (like putting modifiers in the correct place).
• Rules about capitalization of sentences and proper names (which includes names of locations).
• Rules about how to end a sentence (which would also apply to sentence fragments).
• Rules you don't understand why they should be used where they're used.

Before you get mad at me for that last one, that's the ideal situation. If you don't understand why a rule applies, you won't be able to understand (or defend yourself) when you don't apply it. It is possible to tweak the rules "by ear." Unfortunately, it's a bit hard to hear punctuation marks. (Possible, but difficult, and cues vary among people, but that's a topic for another time.)

Rule-bending by ear can work for grammar in places where the rules are allowed to bend, but use your critical thinking. Any English speaker can read an intentional fragment and pick up the thought. but fi you lose yur speling capitalizashon an punshuashun peeple wont bee happie not manie peeple will undurstand u

After making that point, I'd better flee before you lynch me.