The value of human life would dwindle to the point where summary executions are sometimes favourable over bothering with a trial or even a cell, or rioting citizens would simply be mowed down. The homeless and other undesirables in society would be used in human experimentation against their will. If you're unable to get or hold a job, which is extremely likely in a high population low resources scenario, you would probably meet the same fate. If it's far enough in the future, people might be transformed into cyborgs who aren't in control of their own minds, like the criminals turned space marines with neural implants in Starcraft, a process which would form the main body or at least the backbone of the military. Worst of all, though, people like me who want to avoid human contact would suffer, having no place to live in relative isolation. People would likely be more aggressive in order to climb above others, because providing a "safety net" for an enormous population when the world is completely devoted to resources for humans is unlikely.
I am an edgelord, though, so take what I say with a grain of salt, perhaps somehow a world with such a high population and near ecological collapse wouldn't be so brutal.