To indulge/vent an urge that society does not approve of -- this can be fighting, partying, drinking, having sex, smoking pot... whatever. It implies that there are other times when you're a "respectable citizen" and repress the urge -- full-timeparty-animals are not getting their ya-yas out because they always act that way.
Example for ya-yas, to get out:
"I have people flipping me off all the time but because I'm from New York, I get my ya-yas out that way and I get to flip 'em back." (quote from BBC News article "Environment drives Hummer vs Hybrid row" 1 June 2004)
When you gotta shit so bad that the shitpops in and of your arsehole as if convulsing. See Prarie Dog or Seismic Fart.
To wanna shit really bad, but have to hold on while farting your guts out rotten!
To be prarie dogging while farting.
To paint your undies with a brown skidmark and flavour the room with he scent of shit.
I was sitting on the train when this guy moaned, "rat trying to get out!"
"Next thing I knew I was on the floor choking to death, passengers were jumping to their deaths from the moving train and one woman even stabbed herself to death with her knitting needles to save herself from the filth in the air!"
"While coming out of a coma in hospital the nurse said the papers called it, The Seismic Fart of the Century!"
The origin of this sentence is in Hebrew.
State that the person disagree with a certain thing, or something seems wrong, so that the person want's to express his disfavors.
He: Let's get this women to dance for us.
She: I want to get out buffer.