Make sure your fly isn't open, don't swear, don't talk about waking up in the gutter Saturday morning after a fun night out. Don't ask the interviewer out, no matter how hot she is. Don't make a sound with any part of your body except your mouth, and by that I mean words, not whistles, clicks, pops, etc. If they have sports paraphenalia in the office, don't make fun, (on a side note, if they have hawkeye memorabilia around, just get up and leave, it's not worth it). Shave, wear a tie, be yourself, assuming you aren't a mass-murdering pedophile, and chalk it up to gaining experience interviewing if you don't get the job.