Fam

Address your peoples (the homies, classmates, colleagues, etc.) directly.

Usually used before a reason y the person who said something first said something that made no sense.

Example 1:
Random 40-year-old man on Omegle giving himself a hand job: "Show your pussy for more dick!"
The girl on the other side: "NAHHHH FAM!"

Example 2:
Teacher who sees all the girls jumping on their desks and yelling and gossiping and says nothing to them but gets mad at the boys for cooperating on a math problem: "BOYS, WE DON'T DO THAT IN THIS CLASSROOM, GO TO THE PRINCIPLE OFFICE NOW!"
Boy 1: "Fam! Those bitches have been YELLING AND BOUNCING OFF THE WALLS and y'all gonna get mad at us? NAHHHHHH FAM!"
Boy 2: "Yea fam that's fuckin messed up bitch"

Cap

Something someone says that EVERYONE knows is a BIG ASS LIE. Usually used to try to flex by FIBBING. You can tell cap apart from no-cap by just seeing what the person who said it looks like, or if it's just completely unreasonable.

Person 1: "Hey guys I just landed a bottle flip from the top of the Twin Peaks.
Person 2: "THAT'S CAP BRO!"
Person 3: "STOP THE CAP!"
The Karen: "ALL OF YOU JUST SHUT UP! I'M CALLING THE MANAGER!"
Person 2 and 3: "NAHHHHH FAM THAT'S CAP!"