The college interview has no set rules about what a man should wear. In general, college interviews are less formal than a job interview, so a suit and tie are not required. However, you do want to look nice, and what you wear should be dictated partly by the weather, the context of the interview, and the type of program and school to which you are applying. If you have doubts, simply ask the admissions office -- they can easily tell you what type of attire is typical.
You can also read about women's college interview dress.
1. A Suit Usually Isn't Necessary
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If you're applying for a job, you should definitely get out the suit and tie. For a college interview, a suit is often overkill. White collar professionals often wear suits and ties, so the dress is appropriate for the interview. College students almost never wear a suit, and the admissions counselors who interview you won't expect you to wear one. A suit and tie can even be detrimental if you're not comfortable wearing them and you don't feel like yourself.
That said, in a few cases a suit might be appropriate. If you are applying to a business school, you'd do well to look business-like. Also, if you're applying to a very conservative college you might want to err on the side of over-dressing.
2. The Shirt
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A nice shirt is key to proper interview attire. Think in terms of buttons and a collar. In the summer, a nice polo shirt or short-sleeve button-down dress shirt is fine. Avoid distracting patterns and colors. In the winter, a long-sleeve dress shirt or sweater is a good choice. Avoid anything that is old, faded and fraying around the edges. Avoid t-shirts.
3. The Tie
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A tie never hurts, but it isn't always necessary. On the one hand, a tie shows respect for the college and the interviewer. On the flip side, college admissions officers know that most 18-year-olds never wear ties. The tie would be a good idea if you're applying to a business program or if you're meeting with an alumni interviewer near your home. For an on-campus interview, a nice shirt and pair of pants will usually suffice. If you do wear a tie, make sure the pattern fits the personality of the school. An outrageous tie could be fine at an offbeat college, but some campus cultures are fairly conservative.
4. The Pants
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Here, as with the other parts of the interview outfit, the context will partly dictate what you wear. Pressed wool slacks aren't necessary unless you're applying to a professional school with a business-like image. In general, a pair of khakis is a good choice. You can look casual but tidy. Leave the ripped jeans and sweat pants at home.
5. Shorts? Only in Rare Circumstances
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If your interview is combined with a campus tour and it's 100 degrees outside, a pair of shorts might be appropriate. In fact, the college will question your common sense if you're sitting there sweating profusely in a wool suit. Shorts should be neat and hemmed. Save those ratty cut-offs and athletic shorts for another day.
In most situations, however, long pants are the better choice. If you're interviewing for a professional program or if you're meeting an alumni interviewer at a place of business, never wear shorts.
6. The Belt
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Whatever pants or shorts you wear, don't forget the belt. It dresses up an outfit and keeps your pants in place. The interviewer doesn't want to see your boxer shorts.
7. The Shoes
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Black or brown leather (or faux leather) is your best bet. You don't need shiny patent leather shoes, but you should avoid ratty sneakers and flip flops. In hot summer weather, a pair of nice leather sandals can be okay if the school has a fairly casual atmosphere.
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No interviewer is going to be shocked by the metal stud through your tongue, nose, lip or eyebrow -- piercings are common sights on college campuses. At the same time, make sure your piercings aren't too much of a distraction. If the tongue barbell clacks against your teeth and makes you lisp, you might want to remove it for the interview. Large rings in the nose or lips can also be quite distracting during a conversation. It's always possible, of course, that you'll get an interviewer who doesn't share your love for piercings, so keep that possibility in mind as you dress.
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As with piercings, tattoos are a common sight on college campuses and they aren't going to shock most college admissions officers. At the same time, if your forearm has the giant word "DEATH" tattooed on it, you might want to consider long sleeves. Anything violent, racist or explicitly sexual should obviously be covered.
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Plenty of men have been accepted to colleges with blue hair, long hair or a shaved head. The interviewer wants to get to know you, so if you typically have a purple and green mullet, you shouldn't feel you need to change your hair style for the interview. At the same time, the campus culture should inform your decision. It would be unwise to interview at a conservative college or business school with a glow-in-the-dark mohawk.