Contours refers to when you climb out of a swimming pool and your shorts cling to your crotch area giving a very accurate 3 dimensional impression of what your meat and 2 veg look like. Particularly embarrassing in large pools with lots of people. Can be avoided, but takes practise. Contours cannot be achieved in speedos for obvious reasons.
Bob: Hahaha look at Mike's contours! No wonder he's so shy!
Mike: Hey! That pool is cold!
Girl: SORT YOUR CONTOURS YOU PERV!