It means when you think you are because of the other things and that’s a result of the consequences from the actions of when you decide you want to do that because of the outside factors of the unknown
Man 01 (to Man 02): Hey, Can't Them Walk On A Steely Cricket?
Man 02: That's what I'm saying, I mean it's absolutely reprehensible behaviour on their part!
In short, this means the person "going on a t-shirt" is going to die. Then, when they die, their homies will wear t-shirts with the dead person's name on it in remembrance, therefore birthing the term "going on a t-shirt"
Person A: You not gon swing nigga!
Person B: Course I'm not gon swing, you going on a t-shirt