The difference between your and you're

Ok, this one should be simple, yet it's a mistake I see WAY too often! 
If you can substitute 'You Are' then use You're.  If you can't then it's Your. 

Your is a possessive: 
Is that your dog?
Your eyes are pretty.
Your grammar is lacking.

You're is a contraction of You and Are:
You're so stupid
Do you know if you're going to the party?

It make take 2 extra seconds to think it out, but please take the time!  Otherwise you WILL be judged and mocked!

When to use 'dreamed' vs. 'dreamt'

According to many sources both are correct. "Dreamed" is more common in American English, while "dreamt" is more common in British English usage. In either case it is the past tense of the verb "to dream." I personally think that 'dreamt' sounds better and I'll continue to use it...although maybe I'll add a British accent!

Swallowed chewing gum does NOT stay in your stomach for 7 years

This is a complete and total myth. Some of the ingredients in gum are indigestible, and like any indigestible substance that is consumed (marbles, coins, jewelry), it will simply pass through the gastrointestinal tract and be evacuated.  Although, the good news is you do not need to search through the evidence to make sure the gum has passed like you would some other indigestible items.  The digestible ingredients in gum do not take any longer than other foods to digest. And the indigestible portion does not "stick" around one's intestines for years.

'A' and 'Lot' are two separate words

This one should be easy.  Alot is NOT a word.  If you have a whole bunch of something, you have A LOT.  If you hand in a paper and don't want to see a big red slash through the middle of what you thought was a word then please start separating them.  A lot. A lot. A lot.

It is NOT pronounced Supposably

This is one of my favorite clips from Friends.  The very last few seconds in particular.  I remember laughing so hard it hurt....and since then I've met several individuals that make the same mistake!
The correct spelling is: SUPPOSEDLY  There is NO 'B' in it!!!

http://youtu.be/5z0Gitlj9bM

There actually IS a correct use of the word Supposebly (capable of being supposed), but most people, including myself have no clue what it is.  So my advice is: Don't use it!!

The difference between baking soda and baking powder

I'm not even going to try to put this into my own words....there's a whole lotta science going on.
Here's the difference between baking soda and baking powder as found on Answer.com:

Both baking soda and baking powder are leavening agents, which means they are added to baked goods before cooking to produce carbon dioxide and cause them to 'rise'. Baking powder contains baking soda, but the two substances are used under different conditions.
Baking Soda
Baking soda is pure sodium bicarbonate. When baking soda is combined with moisture and an acidic ingredient (e.g., yogurt, chocolate, buttermilk, honey), the resulting chemical reaction produces bubbles of carbon dioxide that expand under oven temperatures, causing baked goods to rise. The reaction begins immediately upon mixing the ingredients, so you need to bake recipes which call for baking soda immediately, or else they will fall flat!
Baking Powder
Baking powder contains sodium bicarbonate, but it includes the acidifying agent already (cream of tartar), and also a drying agent (usually starch). Baking powder is available as single-acting baking powder and as double-acting baking powder. Single-acting powders are activated by moisture, so you must bake recipes which include this product immediately after mixing. Double-acting powders react in two phases and can stand for a while before baking. With double-acting powder, some gas is released at room temperature when the powder is added to dough, but the majority of the gas is released after the temperature of the dough increases in the oven.

"I seen that" is never, ever, ever an acceptable sentence

The first time I remember hearing this sentence was while working in a certain city....where I heard it a LOT.  These were college educated people working in a business setting.  I stopped trying to correct anyone because they all seemed to have forgotten what they learned in school and just gave me blank stares.  (I suppose it was also because it's kinda bitchy to correct people's grammar all the time!)

I left that job several years ago and the offensive sentence seems to have followed me.  There was even an instance that my own husband seemed to have uttered these words although he swears we just didn't hear the 'have', as in 'I have seen that'.  It's still up for debate. 

You are welcome to use the phrases "I have seen..." or "I had seen...", but do NOT under any circumstances leave out these verbs.  Seen is the past participle of the word See.   The past participle is used generally as an adjective describing a finished action.   The word Seen NEEDS its verb!  I don't require that you remember all of the rules, just that you say it correctly to save me from the evil chills that run down my spine when the wrong words are uttered.