BYO...

Student #1 (to me):  "I have to take my mom to the airport tonight."
Me:  "That's nice of you."
Student #1:  "Yep, she is going to be gone all weekend."

(Student #1 then decided to make an announcement to the class)

Student #1:  "Party at my house this weekend!"
Student #2:  "For real?"
Student #1:  "Yep, it's BYOB!"
Me:  "What does the "B" stand for?"
Student #2:  "Bongs."