The "good" fats are those that are naturally occurring - you could go out and "get" fat from them with the tools you probably have in your kitchen. The fat in meat, the fat in nuts, the fat in foods like eggs and avocados and milk (butter) and olives. You KNOW those foods are fatty when you bite into them.
BUT, when you're discussing the fat in meat/eggs/dairy, there's also a difference in the fat between an animal that was fed a conventional mass-produced diet, and an animal that was fed the diet it evolved to eat. Cows evolved to eat grass/hay, and grains make them ill. Therefore the fat that comes from a grain fed cow is not going to be as healthy as the fat on a grass-fed cow... it is still healthier than margarine though, IMO. Chickens evolved as free-ranging omnivores, eating bugs and seeds - a chicken that is fed a strictly grain diet or one that is fed animal by-products (like beef bone) while being confined in a cage is not a healthy chicken, and therefore the fat in their eggs (or meat) is not as healthy as that from a chicken eating their intended diet.
The "bad" fats are those that are man-made, or require severe refining to get - soy, corn, cottonseed, canola, etc. None of those items can be turned into oil in the everyday kitchen. And of course anything that is not in the form it was created in - like hydrogenated liquid fats.
Peanut is one that falls into both categories for other reasons - peanuts are prone to toxic mold, and while you can make peanut oil in your kitchen, it's probably better to avoid it for toxicity reasons.