Somewhat dismissive term for an American male who is an anachronistic throwback to the 1950s; not a teen rock-n-roll enthusiast of the era, but the parent of a Boomer.
Typically conservative WWII vet, tangentially racist ("those goddam xxxx are taking over this country, I swear"), heavy drinker, generally a member of a bowling league and of the Elks, VFW, KofC or Moose from the 1950s through the '70s. Probably still keeps bowling trophies from that era on a china closet in the dining room.
Sadly, a dying breed in American culture.
Original reference credited to Ren & Stimpy animator John Kricsfalusi, referring to his character "George Liquor" as "a real Lodge Brother from the 50s." In more familiar terms, think Flintstones or Ralph Kramden.