"-Hey dude, you got some beef? You want some beef from me?"
"- No thanks... I'm vegetarian!"
Okay, so listen up. This dude asks another dude if he wants "beef," right? But "beef" can mean two things: actual meat, or like, a problem or fight. The second dude is all, "Nah, I'm good, I'm vegetarian." See, he took "beef" literally as meat. You probably wouldn't get this since you are probably a vegetarian.