I wonder what they talk about when no one is around

Looks like shaggy ink caps, but you would need to confirm that yourself.

Probably one of the C. comatus varieties since it’s the typical size in the typical habitat.

Identifying most other Coprinus to species is pretty specialized knowledge in the first place and your post doesn’t have nearly enough information to do so. At the very least we’d need the location and closer photos including a cross section since that’s the only way to see the gills on a Coprinus.