Trakky bottoms (1) make you look like a scouser who has come to steal the aircraft's hubcaps, and (2) may well be made of nylon or some acrylic substance which burns vigorously and melts into skin. Bear in mind that in a light aircraft you are strapped to a big bucket of petrol. This is one reason for wearing natural fibre jeans or chinos, and leather shoes or boots, not placcy trainers, as well as an excuse for posing around in a leather jacket (assuming that it is not a trendy Gucci number full of flammable dye).