Here are some options.
- Teach an honors class. - Even if you weren't in honors yourself in college, just teaching a class of really bright kids makes you seem smarter than them.
- Keep lots of obscure theoretical books on your shelf. Used copies are best, because it they look like they been read diligently even if you've never bothered to open it up.
- Learn all the different ways to call something "pedantic" and use these terms when discussing works by popular scholars.
- Be cynical. For some reason, most academics equate cynical with worldly and smart. So look for the negative and hidden agenda in everything some other department, the college's administration, or the government suggests.
- Wear glasses. Tell people that you used to have 20/20 eyesight until graduate school. They will think you've read your way to being near-sighted.
- Hang some obscure Bizzaro comic on your office door. People won't get it and they'll be too embarrassed to ask you what it means.
- Get your news from some alternative news source (not NPR or CNN or the New York Times) this way you will always have an opinion on things, but people won't recognize that you stole it from someone else.
- Adopt an absent-minded professor persona. If you forget little things like meeting times, where you parked your car, how to use the internet, etc. it suggests its because you have bigger and more important theories on your mind.