Those are general statements though. If someone is bugging you and you want to say you're busy and can't help him this would be better: "Ik ben even bezig, vraag 't aan iemand anders." (I'm busy at the moment, ask someone else.) Or if you're more annoyed: "Zie je niet dat ik bezig ben met iets?" (Can't you see I'm busy with something?) Or if you're super annoyed: "Gast! Ik ben bezig, flikker op." (Dude! I'm busy. Piss off.) Clearly the last one is offensive. :P