My Ban on Speakerphone

This week I am representing someone who is being accused of saying something on speakerphone. He didn't know he was on speakerphone and he didn't know others were listening. Now I am tasked with putting such conversation in context.
I use the Bluetooth in my car. It is convenient since it allows me to speak without my needing to hold onto the phone. Hand held jibber-jabber in the car while driving is illegal anyway. I, however, always drive alone so there are no interlopers. The other day, I phoned a friend who was at work. Generally, I will hang up and promise to call later, but for some reason he put me on speakerphone and opted to continue the conversation. His client had heard about me and wanted to hear me speak. Then, without any warning or provocation, she joined in the conversation.
I don't welcome this. It's a form of rudeness. It assumes a level of friendship that doesn't exist. And her brashness included language that I didn't welcome. She addressed me as, "Dude," which is a big no-no where I come from. I'm not vacationing on a ranch. And while I am originally eastern by birth, I live a hippie lifestyle. Anyway, after her second interjection I said, "Obviously this isn't a good time for me to be calling. I'll speak with you later. 'bye!" and I hung up.
To me, this is akin to recording someone without his knowledge of this in advance.
So I sent him a picture postcard today and asked him never to put me on speakerphone again if he is not alone. Let's hope he can commit!