Squonk
A flood of plumbers
A greed of lawyers
A steam of turds
An abandonment of orphans
An annoyance of mobile phones
A compromise of senators .....
Bob-Dubery
One that I remember is fairly recent and may have some resonance for some forumites.
An attitude of teenagers.
singemonkey
A caravan of Django imitators.
PeteM
A harmony of guitar forum members. :-[