I was recently told the term "hump day" began at DuPont Chemical in the 60's. Roy Mann coined the phrase at the water cooler one morning and it caught on with the guys. It seemingly spread from there. I cannot verify this claim, and if anyone can please throw a post up here.
In fact, I may have started this phrase at Allied Clothiers in 1962 when I first came to Kansas City, went to B.O.P. The next year. By the way, I am Frank Berry!
It has to do with getting over the hump. Monday and Tuesday are in the beginning of the week and Thursday and Friday are at the end. Wednesday is in the middle and it's all "down hill" from there. It is not a phenomenon.