Tunisia is an Islamic country, and although it is probably one of the most liberal countries in the Middle East, people do tend to dress more conservatively than in Europe. Tunisian women all over the country don't always wear headscarves, and most dress stylishly in the latest fashions...but you rarely see a Tunisian woman revealing much flesh. Shorts and short skirts are not worn, neither are low-cut sleeveless tops. For men, again shorts are not the norm, unless you are doing sport. Tunisian men don't walk around town bare chested either. Have a look around you when you arrive, see what locals are wearing and do the same. There's no need to go over the top and cover every part of your body in multiple layers...this is not Iran! But if you dress modestly, nobody will find it offensive, and women will find the amount of hassle decreases dramatically.
Of course, the beach is different, and nobody expects you to cover up on the sands. Even some resorts are used to sunbathing foreigners walking around wearing very little...just when you go into town, put some clothes on!
Tunisia in the holiday brochures always looks sunny and hot, but don't underestimate just how cold Tunisia can get in winter and even spring. I was unprepared for snow in March in the region around Le Kef, and it was cold and wet in tunis in April...it may not be as cold as parts of Europe, but buildings often don't have adequate heating so it can be very hard to get warm! Bring some warm clothing for the colder months, and an umbrella may also be useful. Although the desert regions are still warm in winter during the day, the temperature drops quite dramatically at night.
Traditional clothing in Tunisia is still worn by many older Tunisians. Old men still like to wear their red chechia hats (similar to a fez), often with a burnoos (a sort of cloak with a hood) around their shoulders. You'll see many women around wrapped up in white shawls, sometimes held in place by their teeth. This is the sifsari, similar to Sudan's tobe and India's sari.
Local Customs: Tunisian Hospitality
I was glad to see that hospitality is alive and well in Tunisia...although it may seem in the tourist resorts that everyone is out to get your money or sell you something, away from these areas people are generally very friendly. I noticed this more in Le Kef than in anywhere else, but maybe that was just my experience, as I'm sure other towns are equally as friendly. Everywhere I went in Le Kef, people wanted to talk to me. Everytime I sat in a cafe, people came up to me to chat and insisted on buying my coffee. Some went out of their way to show me places I wouldn't have discovered had I been on my own. To cap it all off, my friend Yasser insisted I travel with him to Gabes and stay with him and his housemates. Even though Gabes was not on my list of must-see destinations, it was a great opportunity to get to know some Tunisians and was one of the more memorable moments on my trip.
While there will always be some who get to know you for other motives (money, sex, visas), usually it doesn't take long to work that out, and just remember that that can happen in almost any country. So don't be shy...if a Tunisian talks to you, talk back!