Some a-holes keep calling you even when you're on another call and they know this [COMPACTIDEA]

You're talking to someone on your phone, and a 'call-in-call' comes from someone else. So far everything is normal. This third fellow cuts his call but then calls you again, fully aware that you're talking to someone on another call [he can obviously hear 'call waiting' tone on his phone]. Then he calls you yet again. And again. And again. He calls so many times that he disturbs and irritates you, and makes you feel that it might/must be something urgent. You're forced to stop your ongoing phone call and call this third person, and it turns out that this wasn't about something urgent, but was a normal, routine call. You grumble and ask yourself, what's the problem in this fellow's life that he wants you to disconnect your ongoing call and attend to him first. Such an asshole. And there are many such shitpots around. I get calls from some such buttholes every few days.