T-Rex: FACT: Every mosquito you ever killed is now a ghost, trying to bite you at all times! And the same goes for spiders!
T-Rex: And roaches. Look, dude, you're just covered in bugs 24/7!
T-Rex: Even when you go swimming they cling to your flesh, hungering and furious. And it's not just bugs! Those birds that flew into your window still haunt you, trying to peck out your eyes with beaks that, LUCKILY FOR YOU, now pass through physical matter. And that's not even considering our dead cave-ancestors: agitated, frustrated, and confused!
Utahraptor: You sure know how to make me uncomfortable in my own skin!
T-Rex: The same skin these ghosts now crave!
T-Rex: And you're lucky ghosts haven't yet figured out how to become real, because if and when they do every living thing will instantly collapse into a puffy pile of red gore as literally trillions of dead but still pissed off animal life pile on top of us.
Utahraptor: Then what happens?
T-Rex: Um, all is quiet on a dead planet and we wait for life to evolve again? IN CONCLUSION, I rate this world-ending threat above "asteroid impact" but below "the dreamer finally awakens and says 'whoah what a crazy yet massively detailed dream'".
T-Rex: (I call her "Lady Sleepypants")!