IA - Internal Affairs - a department of the police who investigate other police. They are often looked down on by other police officers because it is their job to judge if a police officer is doing the job correctly and honestly. Shooflies - a plural form of Shoofly — any kind of fly that is attracted to something and needs to be discouraged with a wave of the hand. We say “shoo” to tell someone to move away from us. So a “shoofly” is a pest to whom we say “shoo fly!”. Combined, it means the speaker feels that the Internal Affairs officers are pests, like the shooflies.