How terrible is international meeting that Putin has to bring his own cup

As one can see in this photo, Putin has both his thermos mug and regular glasses. 

So it's not really about paranoia. According to the official sources, Putin just likes to drink hot tea (or a similar hot beverage) while working. I presume that tea is good for the throat or something like that. Putin is not young anymore, his health is a concern.

But of course, Putin also needs to think about his security. He has a lot of powerful enemies with access to chemical weapons.

And no, that’s not vodka. Nobody drinks vodka from a thermos.