deliberatley low is pretty wierd an unneccessary, i always thought it was skater typeepoplet hat did that, but i saw a 'cool' guy doing it the other day.
however, most people's boxers go above their trousers (the elastic bit at least). when moving about t-shirts often lfit up and they're visible, and i suppose it's better for boxers to be seen rather than midriff, since nobody wants to see that...
...i remember when i went bowling a while ago i saw some loser who was 6 foot tall, but had obviously bought a small t-shirt to show off his non-existant muscles. the result was an exposed midriff. urgh.