Chevy Chase: Good Genes or Good Docs?

Clark Griswold aka Chevy Chase is having the holiday of a lifetime.

Here's the 46-year-old comedian around the time "National Lampoon's Christmas Vacation" came out in 1989 (left) -- and 23 years later, the 69-year-old former "Community" star at an event earlier this year (right).

Hysterical.