When in the library, if someone sits down next to you and starts imbibing then opens up their phone to watch videos with the sound on (no headphones):   this is a cry for attention.  Do not engage!   If you ignore them, they will eventually become bored and move to some other area of the library to bother someone else.   Also, bring headphones.  

I’m sorry you need attention so badly, but I have things to do!