Some expressions of dismissal or insult such as "go jump in a lake" or "take a long walk off a short pier" direct the recipient to fall into a body of water.
Is the figurative idea in such expressions that the person should remove themselves from the scene in a way that is merely picturesque and uncomfortable, or dangerous and potentially fatal? In the first interpretation the meaning is something like get out of here now, or be silent and stop annoying me, and in the second more like I hate you.