There is a theory about socks and quantum tunneling that states that socks actually tunnel to other washing machines and dryers, explaining both the dissapearance of socks you own and appearance of socks that you previously did not own. However, proving this theory would require the assembling of all the washers and dryers in the Universe, marking a bunch of socks and putting them in, and then checking all the washers and dryers afterwords to see if any moved.
Possible explanation for dissapearing underwear: underpants gnomes from Southpark.
Pencils have been known to spontaneously transform into coat hangers; ratio unknown. Somehow, the pencils get some of the DNA of the coat hangers, because if you have all plastic hangers, you usually don't get metal ones unless you have a random mutation due to living under large power lines.
If both socks and pencils transform into coat hangers, but not the reverse, this would imply that the energy state of a coat hanger is less than that of a pencil or sock.
Perhaps there is another dimension in which there is a trapped a being, all alone, who knows that the key to the exit is somewhere in our dimension. So he creates small worm holes from his dimension to ours, sucking out numerous objects, in order to find the key. He sifts through piles and piles of out stuff, looking for a way out of his prison.