LOL depends on a lot of things, left over dinner? but most likely dried cum/ pre cum
One way to get white marks out of black jeans is to dye them black again. You could also use a black marker or pen to color in the white marks. In the future you should wash black jean inside out so these marks are less likely to appear.
They are not white
I would think it could be ejaculation fluid.
white
white
Yes, as long as they are white underwear. Colored underwear/panties/boxers will bleed and lose their coloring.
a boy can shake his legs in his white underwear to help him relax if he stress out
He wears Hanes White Briefs
It probably is semen, or perhaps pre-ejaculate, but it doesn't prove anything. Most guys get erections, and erections often leak pre-ejaculate, which is a clear liquid before the semen comes out. Or it could mean that he has masturbated, also very common.
white
Means nothing.
That's a good question..why do you?