For people who wear glasses...
I can understand that glasses are necessary for certain activities that require improved sight, e.g. reading, driving, etc...however, what is the explanation for mannerisms related to removing and putting back on glasses?
In some cases it is very predictable: people use their glasses to read something and then promptly remove them (holding them in their hand) as they start talking and reading is not necessary at that moment. So you see a pattern of glasses on and glasses off, corresponding to when one reads their notes or a passage and when they address others. In other cases, it seems people remove their glasses to look less threatening (e.g. when saying hello to children); in even other cases, people seem to remove their glasses when they are about to express something rather stressful, or with exasperation or rage.