R

it means ''are'' as in

it is used in group chats, roblox, fortnite, or any game/app where you can chat

R you busy?

MIC rIzZ

Its fancy rizz, as in
Are you a microwave? BeCaUsE i FeEl SoMeThiNG coOkInG uP iN hErE

Let me hit you up with some MIC RIZZ