No worries, it is not graffiti it's dry erase! Notice the two lines are in two separate planes, separated by all the space you are occupying. That looks nice, so you draw another line on the opposite, side wall, going from the car's front to back: You happen to have a dry erase marker and a straightedge in your hands (of course you do!), so you draw a line on the side wall of the elevator, stretching from the top of the elevator car to the floor, complete with arrowheads: The inside walls are all dry-erase boards (how thoughtful!). An elevator is a rectangular prism (six faces, eight vertices, 12 edges, and so on). Please step into our imaginary geometry elevator.
Skew lines have several identifying properties that make the big wooden box impractical: Like a bunch of infinite, double-ended arrows, they would not cooperate. Skew lines are what you would have if you tried to store lines in a big box. You would find the longest line segment and make the box slightly bigger than that, right? What if, though, you wanted to hold rays, or lines? No box exists that could hold either, because rays continue in one direction forever, and lines continue in two directions forever. Suppose you wanted to build a big wooden box to hold line segments. Remember that in mathematics, lines continue in both directions forever.