However, depending on the specific context and the type of untruthfulness you're referring to, you could use these options:
* For liars:
* A pack of liars
* A nest of deceivers
* A band of charlatans
* A clutch of fibbers
* For people who break rules or disobey:
* A horde of rebels
* A gaggle of rule-breakers
* A mob of dissenters
* A crew of miscreants
* For those who spread misinformation:
* A swarm of rumour-mongers
* A web of deceivers
* A hive of fabricators
* A plague of spin doctors
Ultimately, the best collective noun will depend on the specific context and the intended effect you want to achieve.