A Fev
The FEV is the nastiest bug in the Fallout universe. It turns people into freaky monsters and makes them scream like a stuck pig.
I played Fallout and got the FEV. Now I look like a hairless, screaming baboon.
My friend got the FEV and now he has three eyes and a snout.
I got the FEV in the game and now I can't stop eating radioactive sludge.