What does FOS stand for?

Full of s***

When someone uses the slang term ‘FOS’, they’re basically saying that they believe you’re “full of s***”. This is a pretty direct way of stating that they think you’re either lying or not aware of what you’re talking about.

The term ‘s***’ is a bit crude, but it’s often used in slang to refer to lies. So, when someone tells you that you’re FOS, they’re comparing your words or claims to feces, indicating they’re completely untrue or worthless.

Interestingly, ‘FOS’ can also be used when someone is exaggerating too much. Let’s say your buddy claims he found twenty four-foot catfish in one day, you can respond with “You’re FOS”, implying that his story is too far-fetched to be true.

Example for using ‘FOS’ in a conversation

Person 1: Did you hear about that new restaurant downtown? They say their burgers are the best in the world!

Person 2: Haha, you’re FOS! There’s no way their burgers are that good.

Person 1: No, seriously! I read some reviews and everyone is raving about them.

Person 2: Yeah, right. You’re just falling for their marketing hype.