Hair. I don't care about toothpaste, but sink hair is the sign that just on the other side of that drain the fabled drain ferret dangles precariously, carefully manicuring its pelt with an ever-increasing mat of bacteria and other unmentionables. Once I know the drain ferret is there I can think of nothing else. It taunts me. It tasks me. There's nothing for it but to hunt down a screwdriver in order to remove the infestation.
Ha, me too. Dangle-ferret – the greater spotted (yet lesser seen/felt) cousin of the urban dictionary's Dangleberry. Ultimately bros in the sewer hood. I've put myself off my food.
Both. Roaches love to eat dried toothpaste, thus increasing their numbers (I promote roach genocide) and hair is disgusting due to reasons mentioned above.
C. Sink evolution. New species. Survival of the... (I have no words for this.) Guess who has the shortest hair and who opens the pipes in our family.