Ok, I know this idea has been done before, but I have always wanted to write this kind of thing. I'm going to do it for basically every show/movie/book that I like... just a bit of light hearted fun :)
Disclaimer: I do not currently own Supernatural. I have never previously owned Supernatural. I will never own Supernatural in the future.
1) Make sure you carry salt with you everywhere – you don't know when you'll need to line the windows and doors with the condiment, so you can ward off a demon attack.
2) If you see a little girl with freaky white eyes, don't stand around and debate over killing her. Either run away, or do it – chances are, the demon will leave the little girl's body, enter your friend and then let hell hounds attack your brother.
3) Don't blame Sam for starting the apocalypse – he'll get upset, and defensive.
4) Don't blame Sam for Jessica's death – he only dreamt about it before it happened.
5) Don't blame Sam for not killing Ruby either – he didn't know she was lying (although his brother had his suspicions).
6) Drinking demon blood is fine, as long as you're doing it for the "right reasons".
7) Make sure that you don't remind Sam just how many times Dean has almost died – it'll make him upset.
8) When the brothers are in an epic demon battle, don't pull out your iPod to show them a new song.
9) Don't text them either.
10) Sam probably doesn't want you to use his laptop to bid on stupid items on e-bay, especially not with his credit card – remember how annoyed he gets when his own brother uses his laptop?
11) Don't make deals with the crossroads demon. You'll just end up being dragged back out of hell again, but the world will be pretty much falling apart. Plus, then you have to hang with angels, and sometimes, they're worse than the demons.
12) Don't go to a mystery spot. Chances are, a trickster is waiting to make Dean die hundreds of times. It's not fun to watch.
13) When Dean screams like a girl, don't record it and show it to him later.
14) Don't take any hunters to see a supernatural movie. They'll hate it for being inaccurate – after all, the vampires in their life don't sparkle.
15) When Sam and Dean check into a motel, don't be the person that asks them if they want a double bed.
16) Don't burn Castiel's trench coat. He loves that thing.
17) Although you may think that wearing black contacts is hilarious, Sam and Dean probably won't find it funny.
18) Hiding the Impala and pretending it got crushed will only make Dean depressed. It's his baby.
19) Stealing the Colt won't go down well.
20) Neither will calling the police when Sam and Dean are digging up a grave.
21) Don't bother calling John. He usually doesn't answer, even when it's really important.
22) Calling Sam Sammy is a quick way of annoying both Sam and Dean.
23) Dean is the one that dies/almost dies the most.
24) He is also the one who gets into trouble with the law the most.
25) And he likes to make deals with crossroads demons, despite the fact that he hates it when people do that for him.
26) Sam will always win paper; scissors; rock. Dean has a habit of choosing the same option again and again.
27) Dean likes one night stands. Sam is emotionally damaged after the death of Jessica. He prefers to keep people out of his lifestyle now e.g. Sarah, or Madison (although Madison isn't really his fault - after all, she was a werewolf)
28) Driver picks the music; shotgun shuts his cake hole.
29) A bacon cheeseburger is an acceptable form of breakfast.
30) When things die, they should probably stay dead. It causes trouble if you mess with that kind of thing.
31) When in trouble, calling Bobby is usually the answer.
32) You should trust your brother over a demon – even if said demon saves your life.
33) Drinking a purple nurple is not a good idea.
34) Shape shifters like to cause trouble for Dean, usually with the law.
35) Dean, however, thinks it would be cool to witness his own funeral.
36) Supernatural screen caps usually catch Dean/Jensen with weird facial positions.
37) There is always something after death in the world of Supernatural.
38) Sam may openly admit that he wants to be normal, but secretly, Dean wants it just as much.
39) Don't mess with Dean's music – there is a large chance that he will kill you.
40) Dean doesn't like chick flick moments. After all, he is not a woman.
41) Sam pouts – a lot.
42) Dean may be lacking a verbal filter.
43) Dean doesn't do shorts. He hikes in jeans, with M&M's as provisions.
44) Don't let your father run off to meet demons with a knock off Colt. They'll probably know the difference.
45) God is missing. No one knows where he is.
46) Sam's pretty much a genius. Oh, and the yellow eyed demon thought he was special. Now the devil thinks he's special too. We should be worried.
47) Dean has the worst luck in the world. I mean, his dad (possessed by a demon), rips him apart. Then he gets hit by a truck on the way to the hospital. Then his dad trades his soul for him. Then he's ok for a while... until his brother dies. So Dean trades his soul for his brother. Then he goes to hell; and tortures people. In between all that, he gets killed about a hundred times, and almost dies a few more times. If you have bad luck, or are clumsy, stay away from him.
48) Do not leave Sam alone after he's lost a rabbit foot. He'll just get himself caught by vengeful hunters.
49) Bella is not to be trusted. Same goes with Ruby. And Lilith. It's probably safer to just stay away from women at all costs.
50) If Sam has a dream about you dying, believe it. Don't make fun of him – it'll just make him upset when you actually die.