When someone feels something is distasteful or does not agree with something. Usually an act, but can also be characterized as a more general subject, such as an area or a group of people.
Person 1: Can you believe Mark did that to Molly?
Person 2: Yea, that shit ain't sweet.
OR
Person 1: The murder rates in Chicago are rising
Person 2: Shit ain't sweet out there.
Hym "If God didn't say it then it's just a sweet suggestion! And he didn't say it did he? Are you God? So... No... Good suggestion though. But you're not God so I don't have to listen to you."