Cheers co-creator and director James Burrows reflects on Kelsey Grammer's audition tape for Frasier Crane and how it was the smile that caught their attention.

Source: https://screenrant.com/cheers-show-kelsey-grammer-casting-memories-director-response/

Diane and Frasier (Friane, if you will) only date for a year on the series, but it was enough for Shelley Long to show back up in three episodes of Grammer's spinoff.

Source: https://www.slashfilm.com/1418454/frasier-guest-stars-want-to-see-reboot/

So perhaps Grammer's tongue-in-cheek remarks had a hint of sincerity to them?

Source: https://www.slashfilm.com/1452879/frasier-co-star-frustrated-kelsey-grammer/