What's unclear? The guy got a new job. His mother heard he got a new job. His mother went up to his wife and told the wife to her face that the guy was going to divorce her useless ass now that he had a new job. Really, if you can't understand this, maybe you should pay more attention in English class.

Wow, really? I should 'pay more attention in English class'? That's really funny to me, but I'm not going to bother being an internet superhero and bragging about my scores. I will say, though, that if you act like a twelve year old then you're going to get treated like one. The issue with the phrasing in this FML is in its ambiguous nature. "Apparently, my mom heard that I finally got the great paying job of my dreams, and told my wife I'd finally kick her "useless ass to the curb." " Because there are two females being referenced, the word 'her' could mean either one. Also, there is a lack of reference to the speaker for kicking someone's useless ass to the curb. OP could have said that to his wife about his mother, which prompted the mother, who overheard, to confront the wife later. He could have said it to his wife directly, ie "you're history, I don't need you anymore now that I have this great job" which led to a clash later between the mother and the wife. The other option is where the mother has gone to the wife separately and told her that OP is going to get rid of her because of his new job. Any of these options DO make sense, and can be lifted from the phrasing, so don't spout crap about them being illogical. If you don't understand, maybe you should pay more attention in English class.

It's not ambiguous in the least, provided you use actual logic and comprehension. Why on earth would the wife get into a fist fight with the mother for referring to herself in that situation? That would make no sense whatsoever. Use your brain.

"Why on earth would the wife get into a fist fight with the mother for referring to herself in that situation?" ...what? I don't know what you mean with that one but there is nothing illogical or worthy of instant dismissal about the interpretation that OP told his wife he was done with [his wife] and then she's gone and fought about it with OP's mother, who for example may not like the wife. Assumptions about 'background information' like that are things you make with pretty much every FML, so don't act as though the interpretation you consider to be simplest is the only one that makes any sense.