Origin of "scumbag"

scumbag "condom," by 1967, slang, from scum + bag. Meaning "despicable person" is attested by 1971.

^Etymonline

I found a condom reference back to 1939 in this snippet from the American Journal of Orthopsychiatry, Volume 9. The date seems accurate:

And I found this figurative use of the phrase from Chandler Brossard's 1953 The Bold Saboteurs:

What a scum bag of a world it was, what a miserable rat's life. I was getting so depressed I was forgetting the money in my pocket. In the early evening we all broke up. I told the fellows I might see them later at Sinbad's Bar

(See @Kit's comment above for current usage.)

I found an earlier reference for scum-bag as a straining bag used when refining sugar, described in 1819's The Cyclopædia;: or, Universal Dictionary of Arts, Sciences, and Literature, Volume 34 by Abraham Rees:

Having kept it simmering for several hours, and having provided a cooler or receiver, over which is placed a strong wooden frame, and upon this a basket, to which a coarse bag, called the scum-bag, is fitted, he pours the contents of his pan into this basket and bag; and then the mouth of the bag is drawn up, and well twisted together, and a strong board, called a scum-board, is laid upon the bags, with several weights upon the board, to press down the scum.

Etymonline notes scum is early 14th century from foam or froth and:

Sense deteriorated from "thin layer atop liquid" to "film of dirt," then just "dirt." Meaning "lowest class of humanity" is 1580s