If you have suggestions for making a Paranoia group more paranoid I'd love to hear them.
The usual way to turn them into backstabbing freaks is to force the issue. You have mounds of NPCs - briefing officers, PL&C drones, anyone of higher clearance they run into, as well as Friend Computer itself, to force the PCs into throwing each other under the bus.
For example:
Briefing Officer: Friend Citizen! Your regulation jumpsuit has a smudge upon it!
PC: Um. Oh. Sorry!
BO: Why, citizen, is it smudged?
PC: Well, we were in a bit of a scuffle before we got into the briefing room.
BO: And your Hygiene Officer? Where was he in this scuffle?
PC: Um, well... he was in the scuffle, sir.
BO: So, your Hygiene Officer was derelict in his duty, committing unsanctioned violent acts (we shall have to review the tapes from the Communications Officer) and has not been keeping your troubleshooting team up to regulation standards of cleanliness?
PC: Oh, no, sir! It isn't his fault...
BO: Then, you maintain the smudge, and the resulting failure to comply with regulations is all your own fault? Of course, I need not remind you, who are the Loyalty Officer, that failure to comply with regulations is treason! So, citizen, which of you is responsible?!!
PC: ...
They learn, very quickly, that trusting others is a good way to die.