I was an EA leisure flyer and I never flew DL until I got a new job in the fall of '78. About a month into the job I was told to do something in Atlanta day after tomorrow and to call the TA that the company used for a ticket. Not knowing the procedure, I simply said "Newark to Atlanta early Thursday and the last flight back."
When the EWR-ATL ticket was delivered, I noticed that it said "F" class but just went about my business and never said a word to anybody. I subsequently found out that the TA had been instructed that company executives flew in first and they figured that I must have been one.
It turned out to be a job with heavy travel, nobody ever told them anything otherwise, and that is where I developed the front cabin habit for which I have never undergone any addiction treatment.
BTW, I do remember that it was a 727.