Chris Christie's first stint as a sports talk radio host was more like a boxing match -- trading blows with callers over BeachGate ... with one guy telling him to take his "fat ass" to a beach where ALL his constituents can sunbathe.
Christie was guest hosting/auditioning for Mike Francesa's legendary sports talk show on WFAN in New York -- and was mostly keeping the topics to sports ... until they opened it up to callers.
That's when Mike from Montclair (a regular caller on the show) blasted Christie for last week's NJ beach scandal .