Source: This Psychology Today Article
Do you do any of these?
• Appearing weird. Bizarre, too fashion-forward outfits, lots of piercings, tattoos, etc. Of course, some brilliant people are visually unusual, but most people feel that avant-garde appearance doesn't appear intelligent.
• Buying items that clearly aren't worth the money, especially if you're not rich: Coach purses, Rolex watches, BMWs and Jags, expensive jewelry, etc.
• Frequently using a vague phrase instead of a specific, for example, I like boating, camping, and stuff."
• Insisting on following the rules with too few exceptions. Intelligent people weigh the risk/reward of breaking a rule on a case-by case basis and consider possible alternatives.
• Insisting you're correct in response to a more intelligent counter. In such situations, it's tempting to defend your position (and self-esteem) but your listener(s) may well think you're too stupid or stubborn to realize the other person's position is smarter.
• Make basic grammatical errors. "I don't worry about nothing." "He sings good." "He was not hardly finished."
• Make black-and-white statements when gray is required. That's especially dangerous when you're not an expert. But even if you are, more often than not, nuance is required. For example, it's risky to say, "This is right." Safer: "While I've seen cases in which this is wrong, for example, X, usually it's right." Of course, there are times to be definitive. Just be sure the risk/reward ratio is good.
• Mispronounce words, for example, "heighth" instead of "height," "nucular" instead of "nuclear," "excetera" instead of "et cetera," "irregardless" instead of "regardless," "jewlery" instead of "jewelry", "Febyouary" instead of "February", "libary" instead of "library," "duck tape" instead of "duct tape," 'aks" instead of "ask."
• Notably spending a lot of time and money on appearance. Smart people generally think, "If you're devoting that much to your wrapping, you may be trying to hide the product inside, or at least that you use your time and money poorly. Facebook's Mark Zuckerberg famously explained why he usually wears the same gray tee shirt: "I really want to clear my life, so I have to make as few decisions as possible about anything except how to best serve this community,"
• Rambling utterances. Smart people are usually concise and when speaking for longer than a minute, make the structure of their utterance clear, and they don't ramble off-topic.
• Saying you believe in fate, for example, "It was meant to be." "Things happen for a reason." "Maybe it's a sign."
• Smoke tobacco. Today, not only is smoking clearly dangerous, it's become uncool. So anyone who smokes in the face of that is widely viewed as less than Einsteinian.
• Sound cock-sure of yourself when you often turn out to be wrong. Consider your track record. Are you often enough right or at least defensible?
• Starting a written message with, "My name is." Your first sentence is your first impression. Leading with "My name is..." is far from optimal. First, it seems a bit narcissistic -- Your name isn't of great interest. Worse, it's redundant. Your name appears at the end of the message and, in an email, in its "From" line.
• Substance abuse. Sure, many people will smile at the drunk or pothead, but most intelligent people privately think you're not smart for abusing a substance.
• Talk about your superstition, for example, you think black cats are bad luck, Friday the 13th is dangerous, or that our fate is written in the stars.
• You admit to seeing a psychic, using tarot cards, talk about your astrological sign or horoscope, and/or that you believe in past lives.
• You gush about pop culture: adoring a celebrity, sitcom, or sports team.