Ted's dad:
Watches Bill and Ted disappear in the phone booth and immediately return with his grandchild and knowing how to play.
Arrests DeNomolos, a literal super villain from the future.
Watches his son's band become world famous with the literal grim reaper on bass.
Sees evil robot bill and Ted from the future blow up in front of him.
Attends his daughter-in-law's birthday parties where they regularly state they are over 500 years old and from medieval England.
And still doesn't believe they traveled through time or went to hell.