They don't eat out together often, it is maybe once or twice a year that they eat out at a restaurant, despite the fact that they have at least two meals together nearly every day. At work they have take out, normally burgers, pizza or Chinese, sometimes soup or a sandwich, it really all depends on whether they are stuck in the office, or what place was closest for someone to pick up food for them all. When they are at Gibbs' house they often have take away as well, Thai, Chinese or pizza. Sometimes Tony will cook up some Italian meal, his Lasagne is one of Gibbs' all time favourites, or Gibbs will make cowboy steaks in the fireplace.
Eating meals together is common, but it is normally in the busy work environment or in the quiet of Gibbs' house. Eating out is neither of those things, it isn't a non-busy environment, but they can sit and enjoy the feeling of being able to sit calm while waiters, waitresses and chefs are the ones that are busy. It certainly isn't quiet either, other diners as well as staff all talking about different things. Tony doesn't mind the noise though, it is a change of pace and it is nice to have background noise in case Gibbs decides that it is an evening in which he is being a functional mute.
They reserve eating out for special occasions, having both agreed that they don't need to be out on a date at a restaurant every other weekend, with their jobs a quiet life outside of work is a relief. Instead they save eating out for when they have something to celebrate, like one of their birthdays or perhaps their anniversary.
They always go to the same restaurant when they go out for dinner, a little family run Italian restaurant that they both agree is the best Italian restaurant they have ever eaten at. Although Gibbs argues that Tony's home cooking is better than what is served at the restaurant, they agree to disagree, although Tony enjoys the praise. There is something about the fact that Gibbs prefers his cooking that makes him preen inside.
Tony knows that the others wonder about their relationship, Tony having seemed to have traded nights out at various restaurants for nights in Gibbs' basement. He has changed over the years, as time had passed he realised exactly what it was that he wanted. One or two dates with a young woman at some fancy restaurant just seems to leave him cold, there was nothing to the dates, it was meaningless fun. Gibbs on the other hand, there is a connection between them, he actually has feelings for the other man.
Staying in is much preferable to both of them than going out to eat, at home they can eat curled up on the couch, or even in bed. Once they finish their food they can move straight on to their dessert, their favourite part of the meal, whereas in a restaurant it is rather frowned upon to partake of their dessert of choice. Normally when they eat out they only have a starter and a main, normally ordering dessert to go. The restaurant they frequent does an amazing tiramisu and an even better coffee dessert, but there is no way they would be able to eat them at the restaurant, not with the way Tony always moaned around his spoon. They were Federal Agents, it wouldn't do to be arrested for public indecency.