I usually say I'm dead.
Is Mr Evans there ?
No, he's dead.
He's dead ?
Yes, dead.
BBbbbrrrrr.
Sometimes I just say Yes to every question or sentence till they put the phone down. LOL
Once a guy from 'Microsoft' called saying my PC had a virus. I went along with it. he got to point where he was asking for me to get into the bios and type in some numbers and stuff. He asked what it says on your screen so I spelled out F.. U ...C......**** Y........O.......U.
At which point he screamed down the phone 'Oh you mother%%%%&&^er ' Lol

You can always tell the scammers. Indian accent, lots of noise in the background. Getting a few from here in the UK though but only takes a couple of moments to guess their game.
I dont get as many these days though. Kinda sad in a way as I used to love winding the scotes up.