5). You become jittery and too talkative.
The most important part of interacting with people is acting like you're interested in them, but in a job interview that's not the case at all. Remember, this is YOUR interview. You shouldn't be asking the interviewer if they have any daughters in college and how big their boobs are and then rail on for 15 minutes about boobs. Even if the interviewer is a guy, usually it doesn't paint a very professional picture of yourself.
4). You display rude behavior.
When you drink too much the line between right and wrong becomes really blurry. I'll never forget the time I got way too drunk before a job interview and went there in a skimpy white dress and did the Sharon Stone leg crossing thing from "Basic Instinct". I'm nearly 100% sure the only reason I did that was because I drank too much and it was kind of funny now that I think back on it, but I really would have preferred the job. Now my chances of ever being a teacher are in serious jeopardy.
3). You become too honest.
Look we all lie on our resume and we all exaggerate during an interview. It's better to exaggerate a little than to undersell yourself. At least if you get the job you can try to live up to your lies which is better than underselling yourself and not getting the job. The problem with drinking a few 40's before a job interview is that you'll start to lose track of your lies and feel like you just need to level with the interviewer. That's dangerous because that's when you start revealing the fact that you didn't really go to college, that you have no real job experience, and that you once accidentally killed this kid you met at a state fair while on a childhood family vacation and buried his corpse in the woods before your family went back home.
2). You will need to urinate BADLY.
This is the most obvious reason to not drink before a job interview. You're going to need to piss and if the interview runs a little too long it might look very awkward to ask to leave to use the bathroom. The interviewer will be wondering why you didn't just pee before you left the house and might figure you have some sort of active bladder disorder which could make you a liability if hired. Worse yet is the decision to just try and tough it out and hold the urine in because the slightest disturbance can trigger a pee storm. It's really difficult to win back the crowd after you've pissed all over your pants and created a puddle in the carpeting of the manager's office. Some people would consider this to be the number 1 reason not to drink before an interview, but I have it as two because there is just one thing worse.
1). You will throw up.
If you drink too much before a job interview you're still going to be a little nervous and that nervousness can create some stomach issues. Add that to the alcohol and it's very likely that you will throw up all over the boss' desk. This is almost an instant end to any interview. In a way it's kind of the best answer to the question "Tell me a little bit about yourself" because they can see all the different types of food you eat, but that's not an acceptable response. It's also embarrassing because you feel obligated to clean it up, but if you try to then it's like you're acting like you already work there and got the job as the janitor. Let the current janitor take care of it. Just get up and walk out. Don't even apologize, you're never going to see these people again. There's nothing you can do at that point except hold your chin up, stumble out, and learn from your mistakes, that is if you're able to recall any of them.
So when you're struggling to remember how to tie a double Windsor, wishing you were dead, looking over to the bottle of bourbon and loaded revolver on your nightstand, remember, drinking probably won't help you get the job.