In America, most jeans are designed for the waistband to ride halfway down your butt, or even at the tops of the thighs, with the crotch part down by your knees. And even if the "waist" (around your butt) is 36 inches, the rest of the pants will be cut ridiculously oversize, like size 60. To keep from being arrested for indecent exposure, brightly colored boxer shorts cover the naughty bits. Cartoon characters like Scooby Doo or Daffy Duck seem to be extremely popular for boxer patterns.
A few extremely expensive jean brands are designed to properly fit... on sufferers of anorexia. Otherwise, jeans are "one size fits none."