Good ol' boy

When you hear someone talking about a 'good ol' boy,' it conjures up the image of a guy who lives in a small, rural town, drives an old beat-up pick-up truck with a Confederate flag in the back window (which he sees as a symbol of Southern pride), probably chews tobacco and may or may not have a high school education. They are perceived to be prejudiced and racist. Calling someone this is not a compliment, unless you also happen to be a 'good ol' boy.'

Example:
-I live in New York now, but back home, I knew a lot of good ol' boys.
-Really?

Douchebag

A 'douchebag' is a serious insult to a guy, meaning he is a complete (fill in explicative here). A douche is a product sold to clean a woman's vagina. This term is extremely derogatory and should only be used in informal situations.

Example:
-My roommate threw up on my bed again.
-What a douchebag!

To go off on someone

'To go off on someone' means to tell someone how angry you are about something they did.

Example:
-So what did she say?
-She totally went off on me, saying how immature and irresponsible I am.