There are two categories of food poisoning (intoxication and infection), and the bacteria causing food poisoning have an incubation time. If you ingest a bacterium that falls into the "intoxication" form of food poisoning, it means that the bacteria has infected the food and you are eating its toxin. It will take about 4 hours for this to make you sick (unless there is a whopping load of toxin in the food, enough to make it taste bad- bad enough that you wouldn't eat enough of the food to make you sick). If you consume a bacterium that is of the "infection" form, it takes a minimum of 6-8 hours for enough bacteria to grow in your system to make you sick. So... if you get sick right after you leave the restaurant, or within an hour or two, it's highly, highly unlikely that you have food poisoning.
You also need to remember that there are some foods that are far less likely to become contaminated, like tomato sauce, salad dressings (oil based), etc. There has to be enough water and protein source in the food, at the right pH, for the bacteria to grow. pH is too high in tomato products, there's not enough available water in oil-based products, etc. for the bacteria to be able to grow. Some bacteria need oxygen to grow, some can't grow if there's oxygen around. Interestingly, food poisoning from things like egg, chicken, and tuna salad isn't really from the mayo. The bacteria is carried in the protein source (or introduced by cross contamination). The mayo coats the protein source and creates a mini-environment where no oxygen is present... and it's this environment that encourages the bacteria to grow. SO, while the bacteria probably wouldn't grow if the mayo weren't there to create the no-oxygen environment, it's not really the mayo that causes the food poisoning.
There are lots of other things that dictate true food poisoning...like temperature of cooking, processing, holding of food, and it's statistically almost impossible for just one person to get food poisoning from a specific food; if you get it, many, many others who consumed this food will become sick, too. I guess my point is to remember to wash your hands and remember that if you are sick, it's most likely from a bug from being on a plane, in crowds, in strange places than it is from food poisoning!
