Gravitas is defined as,

"seriousness and importance of manner, causing
feelings of respect and trust in others."
- Cambridge Dictionaries

It seems to me, however, that there is often a
fine line between gravitas and pomposity.

For example, sometimes a TV talking head strikes
 me as credible and authoritative one moment, and
then vacuous and pompous the next;

and I catch myself wondering when and how he
crossed the line from gravitas into pomposity?

and where is that line?

and what is "pomposity" anyway?

I can't easily define pomposity; but I can recognize
it when it's on display, as in the video below -





the above features humorist Jean Shepherd