Why is coffee called "joe" and Wednesday called "hump day"?

No idea about Joe, but Wednesday is hump day because it’s the middle of the working week. So after Wednesday, you’re over the hump and heading for the weekend.

I think joe is simply a variation of the word java.

“Joe” comes from “jamokka”. Wednesday is “hump day” because it is the middle of the work week’ get over Wednesday and it is all downhill to the weekend!

Actually, “the rain is Joe;
The fire’s Tess;
and they call the wind Mariah!”

There’s a myth that Joe as slang for coffee comes from “Josephus Daniels”: secretary of the US Navy during WW1. He banned the consumption of alcohol on naval bases (as well as other fun stuff that sailors were traditionally known for) so the sailors started drinking more coffee.

The term “joe”, possibly formed from the word “java”, for coffee originated in 1927, no doubt a slang term used by hipsters of the era.
“Hump day” is the middle of the week, so you’re “over the hump” of the work week, sliding down to the weekend.

As far as I’m concerned called Wednesday anything other than “Odin’s Day” is blasphemy.

From World Wide Words on “Joe” -

Q Any idea where the phrase a cup of Joe in reference to coffee came from?

A We wish we knew for certain. The absence of any clear origin for the use of joe to mean coffee has, as usual, led to stories being created to explain where it came from.
A persistent one alleges that it derives from the ban imposed by Josephus “Joe” Daniels, Secretary of the Navy during World War I, on serving alcohol aboard US Navy ships, except on very special occasions. Coffee, it is said, became the beverage of choice and started to be called Joe in reference to him. The problem with this story is the dates. Cup of joe first appears in print in 1930 but the order to ban alcohol — General Order 99 — was issued on 1 June 1914. It banned officers’ wine messes, which had only been permitted since 1893; ships had otherwise been dry since the spirit ration was abolished in 1862. It seems hardly likely that the loss of a wine mess limited to officers on board otherwise alcohol-free ships would have led to a nickname for coffee that only started to be written down 16 years after the order.
Professor Jonathan Lighter, in the Random House Historical Dictionary of American Slang, leans towards another story: that it came from the Stephen Foster song Old Black Joe, with the resultant mental link between black and coffee. It is true that the song — written in 1860 — was extremely popular at one time, but it makes no reference to coffee, so linking the two is implausible.
The most boring, but most probable, suggestion is that it is a modification of java or jamoke for coffee, perhaps under the influence of one or other of the many expressions at the time that contained the word Joe — for example, “an ordinary Joe” (though “GI Joe” for an enlisted man in the US military is from the next decade). It is significant that an early example appears in 1931 in the Reserve Officer’s Manual by a man named Erdman: “Jamoke, Java, Joe. Coffee. Derived from the words Java and Mocha, where originally the best coffee came from”.

Thanks, @zenvelo. And thank you al for your answers.

Joe became a slang term for coffee because of the slang term for a man or a guy. Hey Joe! that sort of thing. Coffee was viewed as a common drink and/or a drink for common folks. so it started getting called “joe”.
Hump day is easy: It’s the middle of the work week. Your work week is a grind…an effort…an uphill climb. You spend Monday and Tuesday going up hill, but Wednesday is the top of hill, or the hump. After that, it’s all downhill to the weekend. You made it over the “hump” and are heading to the weekend.

@seawulf575 Your explanation of “joe” is nice and simple.