From the 70's a lighter version of the term; "Bad Scene," meant to be much less dramatic. It would rarely be used by the person who actually had the experience. Rather, it would be a show of support from one friend to another, though it could also be an attempt to trivialize the experience.
In extreme circumstances, it could also describe an ugly experience with
drugs, violence or sex.
Bummer is a shortened version of bum scene.
The
word 'bum' would often be said while holding in a
hit of weed followed by the
word 'scene' that would be stretched out while exhaling the
hit. As in: Bum (holding breath) sceeeeeene (exhaling slowly).