"say wassup" is something you would say when you join a conversation, or have absolutely nothing to say at all. Saying "say wassup" can be said at any times, there is no restrictions. If you find yourself in a weird situation or a fucked up one. Just say "say wassup" and the conversation will be lit, and from tehre just keep going.
You join a conversation:
"say wassup"
The rest of the group
"say wassup" "say wassup".
You in a weird conversation:
"What do you mean, why you saying that, it disgusts me"
just say
"say wassup" "say wassup"