Talking about common sense could be damned baffling sometimes. Because everybody has different standard to what common sense means to them. Though I would say definition of common sense depends of what kind of mentality you have. I will leave that for you to ponder.
While some people has different opinion as to what is common sense and what is freedom of action or individual rights, let's get very basic as to what is lack of common sense. Believe me they are all around you (if you yourself are not).
1. The room is filled with bright sunlight and some people still choose to switch on the light (does not apply if it's out of your control, centralized switch control for instance)
2. Talking loudly (or making noise) next to someone who is sleeping
3. Talking loudly (or making noise) near to someone who is performing salah
4. (Ever so common) do-not-use-signals-on-road attitude
5. Ordering menus at a restaurant in a rude manner and lack of respect to people just because she's a waitress
6. Waitress who thinks customers cannot always be right and does not even smile while taking orders
7. Walking in a big group in the hallway with a damned slow speed and blocking ways for other people who apparently walk faster
8. Do not smile while saying thank you
9. Do not say thank you at all
10. Squatting on a sitting toilet bowl at a public toilet!
And of course the many other example.
If you did any one above so very often but most of the time you forgot that it is suppose to be a common sense or you did not notice other people are badly affected with your lack of common sense, it's time to self-reflect Ma'am/Sir.
I would say scrolling down smartphones while being at a dining table is lack of common sense. But people with smartphones would state otherwise. Apparently it's what they call lifestyle.
Again with the smartphone issue.