z-dong

Z-Dong is a guy named Zach Herron in a boy band known as Why Don’t We (he made up this nickname on his own)
Dong stands for penis so his nickname is literally penis Zach.

Hey! Have you’ve seen that guy in the band why don’t we?
You mean Z-dong? Yeah he’s great!

fun bomb

A fun bomb is where someone is the life of the party (specifically a girl).

Harvey: “Dang today was so boring I wish the fun bomb was here!”
Jayden: “Ikr I love Stella so much, she is the fun bomb!”