Pretty much the opposite of Goodbye, out of spite just after an argument you say badbye after they say goodbye.
Jonathan:I love the world
Cody: I HATE TURTLES
Leah: Turtles are pretty
Jonathan: No they aren't they're about as pretty as the best kind of food you can make
Leah: I HATE YOU AND YOUR INSULTS YOUR SO MEAN
Jonathan: Yeah whatever goodbye
Leah: NO NOT GOODBYE, BADBYE!!!
Cody: Yeah badbye, because i like the word