Why is it so gross to share a toothbrush? Even with someone who routinely has other sorts of oral contact with you? You can share nail clippers or hair brushes...I'd even put on someone's dirty socks before using their toothbrush. It's not the same with a hair brush. Not thermometers (as long as they get wiped off). I know there has to be something that makes toothbrushes different, but I can't put my finger on it.