Trans fat is the rare case where the goal isn't moderation, it's as close to zero as you can get. Your body has no need for industrial trans fat at all, so there's no amount that's actively good for you.
The reason it's treated more strictly than other fats is how it hits both types of cholesterol your blood carries. A regular intake is associated with raised LDL, the low-density lipoprotein often called "bad" cholesterol because it tends to deposit in artery walls, and at the same time lowered HDL, the high-density lipoprotein known as "good" cholesterol because it helps clear cholesterol back out of the body. Pushing the harmful type up while pulling the protective type down is an unusually unfavourable combination.
It hides in partially hydrogenated oils, and so in some margarines, packaged baked goods, fried fast food, and long-shelf-life snacks. Many countries have moved to restrict or ban it, so it's far less common than it once was, but it's still worth scanning labels for anything listing partially hydrogenated oil. Treat any regular source as worth cutting rather than something to keep within a limit.