I think most people are 'enjoying' the novelty of the toothbrush for a situation which would otherwise be squick-tastic. Seeing Karen acting like a younger Kanbaru was kinda 'o.0' for the first half but then the toothbrush came out and my logic also left....
While this doesn't really do anything for the overall story other than inter character dynamic, it was definitely made to give everyone a 'WTH/WTF/0.0' moment, which it did, regardless whether one actually liked it or not.