Same as "Talkin Shit" Putting a person down with the worst possible words you can think of. Whether they are true or not. It's all about makin them cry.
When people are about to fight they will be talkin as much trash as possible in order to get the other one to back down. It's also used in sports when 1 team will always be talkin trash on the other.
Sometimes, a really shit human being will do the public service of identifying themselves and voluntarily removing themselves from the situation. This is the trash taking itself out.
After Buffalo police knocked down and left a 77 year old protester bleeding in the street, 2 of them were disciplined, and 57 of the Buffalo police resigned from the task force in protest. It's like the trash taking itself out.