One thing I dislike the most is a slacker. 
me too a slacker by definition is someone who avoids work and basically has no work ethic
I'm actually going through that now with someone at work who definitely lacks work ethics. 
That is so hard especially knowing they get paid the same as you and you are working, it is not know for sure but the term started either in 1790 or 1898
Exactly and I  think it is out rages like you are getting paid to do nothing at all there are some hard working people in the world and slackers make them look bad or try to.
during ww 1 they used the term to describe those who dodged military service
So they actually had people in the military that would dodge work. 
I think it was those who dodged the military all together they used it in WW 2 as well in the US