Narrator: WHY ARE POLTERGEISTS SUCH JERKS??
T-Rex: Poltergeists! They throw pots and pans at our heads, knock on walls, and mess with our electronics!

T-Rex: BUT WHY? What'd we do to these chumps??

T-Rex: Originally, our greatest minds suggested that just as we can see through ghosts, they too can see through us, in a figurative sense! They are aware of every lie we've ever told, and so they're super cheezed at being lied to: hence the smashed up plates and what not.
Dromiceiomimus: What about ghosts of people we've never interacted with?
T-Rex: Ah, that brings us to Theory Omega!

Utahraptor: Theory Omega was developed shortly after the internet was discovered, right?
T-Rex: Indeed!

T-Rex: When we saw how normal peeps exposed to anonymity and an audience became TOTAL JERKWADS, scientists began to speculate what would happen if you gave someone anonymity, an audience, PLUS voluntary invisibility and FRIGGIN' FLIGHT POWERS. The result?
Utahraptor: POLTERGEISTS.
T-Rex: Precisely.

T-Rex: In conclusion: your grandma was a peach in life, but in death she's smashing all your stuff up for the lulz, and we just have to accept that.
T-Rex: ...
T-Rex: *sigh*