The Brief: A diss is an insult.

DEEP DIVE
Diss is a shortened version of disrespect.
Your girl a say we cute, if you diss you will get execute –Drake, “Know Yourself”
A “sneak diss” is a shady, weak, behind the back, or cowardly diss.
People will try to squash their beef with you but still sneak diss. That’s why if it was ever bad blood with you, there’s no hard feelings, but still don’t come near me.
— India Royale (@prettyindie) September 19, 2018