This stands for 'shut the fuck up you fucking piece of shit'.
Most people use this word when they are angry or annoyed.
Girl: Omg, Stacy is having an awesome party tomorrow!!!! You have to come!!! There are going to be a lot of really cute guys there and a lot of food and we are all going to play spin the bottle and get locked up in a closet with the other person for 10 minutes!!!! Omg..... <Other girl interrupts her>
Girl #2: OMFG!!!!! JUST STFUYFPOS!!!!!! DAMN! YOU ARE SOOOOOO FUCKING ANNOYING!
slip of the tongue perhaps,
Those idiots who drive around in a ridiculously raised pick up truck, making a top heavy vehicle even more top heavy and unstable
A:*gah*
B: "Whats the matter"
A: This dam prickup is blinding me.
B: Stupid thing's, as if there lights weren't blinding enough as it is.