This morning I caught a little snippet of a cable TV show: Dick Cavett and Mel Brooks, having a conversation onstage before a packed audience, a recently-recorded show. They got onto the topic of Jack, and Cavett told his elevator story. Then Mel Brooks (best as I can recall):
"Years ago I was having lunch with George Burns in a studio commissary. In walks Jack Benny in full American Indian regalia--buckskins, warpaint, the headdress, everything. He sees George and walks toward the table, and George puffs on his cigar and just as Jack approaches, George says, 'Jack. You working?'"
Don't know if it cracked Benny up, but it got a good laugh from Cavett.