Freezing food makes the water content turn into ice crystals. Ice is physically bigger than the equivalent quantity of water; so within the food the water expands and breaks the structure that holds the water. Any food with a high water content is more vulnerable to spoiling when frozen. Here is a list of food items that do not freeze particularly well...
Yoghurt/Milk and Cream - these are only really freezable if you have whipped them first. Even then, when thawed they are never quite the same.
Emulsions - Mayonnaise/Hollandaise because they owe their flavour and consistency created by blending water and oil. When the mixture defrosts the water and oil are separated...not good.
Eggs - In the shell they just burst and leak everywhere. However, interestingly if you separate the eggs first you can freeze the egg whites, or yolks. Never freeze a boiled egg (i.e. on that has already expanded with cooking) it goes weirdly rubbery.
Jelly or Jello - it separates in the same way as an emulsion. The water breaks out and the texture goes nuts (kinda spongey).
Tomatoes - High water content leaves them mushy and awful. Unless you want to peel the tomato, in which case running hot water over the surface of a frozen tomato will make the skin really easy to remove. If you need to freeze tomato think about why. Freezing a sauce or puree is much easier, so why not freeze after preparation?