Granted I know this happened Friday but I’m thinking about it for tomorrow.
Basically I have a nightmare client and when I spoke to him on the phone he kept saying he couldn’t hear me. I raised my voice very loud (to the point colleagues were giggling) and then he started saying - I still can’t hear you. Go on shout as loud as you can! Shout! 
I work in a large open plan office and to be shouting a conversation would be humiliating.
Oh and I’ve spoken to him before and he never complained about not hearing me before (no other client has) and he’d just spoken to a male colleague and could hear him just fine.