You have to actually be nice to someone in your place, even when they're in your way, using your stuff and you just want to be left the hell alone.

You don't own anything anymore unless it's something bad.  Then it is yours and only yours.

If you walk around naked all the time, you get made aware of everything that is wrong with your body and told to put it away OR you're constantly being pawed at when you're just trying to be naked.

You are now completely aware of what things you do that are completely weird when before you could live in complete ignorance and bliss. In order to do weird things, you now have to hide somehow in the bathroom, wait until they're away or go rent a hotel room for an afternoon.

Now there are two people to pick up after. This especially sucks if one of you is a neat freak and simply can't rest until everything is put away.

Another set of parents are around to tell you what to do with your lives, and to try guilt tripping you when both families have events planned and you can't make it to both.

There is always going to be at least one chore that both of you hate doing and therefore you'll fight over it, and be forced to list off ALL the things you do to try to force them into feeling guilty and doing the chore.

Your secret box of secrets now needs to be more cleverly hidden than ever before.

It's easier to tell people off and storm off in a huff when you don't have to pack up all your shit and find a new place to live.

There is now another person to remember everything you've ever done wrong and remind you about it. Even those things that you forget you've done and can't really verify that you DID do them are used against you for years. After awhile you are convinced they're just making up shit.

Existing purely on bread and peanut butter becomes wrong somehow.

They find out you're not all the things you had claimed to be when you were trying to get them to like you.

You have justify spending thousands of dollars on an entertainment system and hundreds of CDs where before you would just not eat for a few weeks to pay it off.

There is someone that knows what and asshole/bitch you are and they still stay around.  That just seems like something very creepy is going on. Why on earth do they stick around?

If there is no toilet paper around when they go to the bathroom, it can only be YOUR fault.

It's always the smallest things that end up driving you insane about them.

You can't tell them off because for some reason you don't want them to leave, even those times you think you do.

You have to put up with their crappy taste in music/movies so they put up with yours.

There are moments you look at them and wonder what the hell you think you're doing with your life.

Listening to music in the car becomes a negotiation deal when you both have different taste in music.

You have to pretend to like their stupid friends and they have to pretend to like yours.

If you start a 'war' of pranks, you have to be ready to fight it for the next few years until one of you gets hurt. By that time it's a 'tradition' and who are you to stop a tradition?

Don't ask questions you don't want answered honestly. You will get an honest answer to "Am I fat?", along with dietary advice to alter the situation.  

They know when you're lying to them after a while.

You have to replace older items with "nice" things.  Apparently duct taped sofas aren't "nice".

You can't drive like a maniac without getting elbowed in the arm.

Finding private time to masturbate becomes more difficult and if you try to include them then you're 'bothering' them all the time.

If you get up to get yourself a drink/snack, you now have to make two or at least ask them if they want any.

You will never again find YOUR underwear, just THEIRS.

When you're sick, it rocks because they have to take care of you. When they are sick, it totally SUCKS because you have to take care of them.

There is always a witness to your stupidity and someone to remind you of it the next day. (and the rest of your life)

You have to argue over what movie to see and can somehow never win because you can go see your movie 'next weekend' but by the time they agree, it's not in the theatres anymore.

Toothpaste tubes become a touchy issue.

For a certain week it's hell on earth for both of you in completely different ways.

Things you used to do that were cute are now called annoying and you're told to stop them.

You have to share the bed with someone after sex.

No matter what, you will always be wearing their socks, yet you don't seem to have any of your own.

You forget what being 'right'  feels like because it all just degrees of wrong. They tell you they feel the same way, so who the hell IS winning here?

There are little notes around telling YOU where things go because it seems you've become braindead and NEED them. So you begin to write your own notes to them.

You are asked fifteen million times where their belt/hat/whatever is every day, and you never know. You've gone beyond even suggesting they put it in the same place each time because that just makes things YOUR fault for suggesting such a thing.

The cat/dog seems to like the other person, and you don't want to upset the cat/dog by killing them.

The first time you tell a story they think it's funny. After a few years, they've heard it a million times and now roll their eyes every time you open your mouth. So you start making things up to seem more interesting and they just shake their head.

You can't always point out odd things they do because they will simply tell you something odd you do. Each time you do this, you realize that you really ARE odd.

There are times you get bored with hanging out with them. You have nothing new to say to each other and just want to be left alone for a bit.

Their stuff sucks and your stuff rocks.