The numbers of people I see wearing their mask incorrectly is quite a large percentage, particularly on TfL services (Overground and tube). Of those people, about a fifth are wearing the covering over the mouth only, not over the nose as well.
Masks 'worn' under the chin is very common. Now even the thickest person cannot possibly believe that is doing any good, or complying with the law. It's fairly obvious that those people don't want to wear a covering, so think they can store it on their chin, to pull up in the unlikely event BTP show-up, or for those periods when they get off the train and want to be seen as 'doing their bit'.
The people on social media may give the illusion that there is widespread support for wearing masks. In the real world, however, the chin-wearers tell a different story.
Frankly, I have more respect for someone who outright refuses to wear one, and is visible about it, than the twits who park the mask on their chins.
I also wonder about the efficacy of a mask worn correctly, but resting on a mass of facial hair, as seems to be the fashion amongst a particular age group. Does a mask worn over a beard really fit tightly enough to be of any use?