Ask them why they're wittering about this risk apparently without evidence. Your colleague is the one making the contentious claim, they are the one who should be backing it up... there should be no burden of disproof!
Or simply join in with the nonsense to make anti-EVers look stupid;
- EVs aren't just inflammable, they are sometimes involved in road traffic accidents!
- Criminals can use EVs as getaway vehicles!
- My neighbour's milkman's son-in-law's cousin drives an EV and he's a well-known sex pest!