phrase used to point out to someone that they are out of their jurisdiction or speaking out of place. Used in instances when someone is making comments or decisions that are not related to their expertise, knowledge base, or responsibility.
Burns: "I wish Marge were here to give me a back massage."
A snitch, tattletale, a rat, basically someone who tells all your business, that one person who will tell the cops on you first chance they get.
Kid A: "Yo, you gotta talk to your girl, man, she's a straight up <i>stool pidgeon</i>."
Kid B: "Why you say that?"
Kid A: "She went and told the cops that I was the one responsible for knocking over mailboxes last weekend."
A man who is an extreme advocate of road rage/road type violence, Enjoys a good bit of banter over a punch up with a cop. I nearly went grand pidgeon on this cunt