I'm going to tell my overweight mother she shouldn't be the judge of my exercise habits
Why would you say something like that to your mother?
She makes me really angry and patronizes me when I try to go on diets.
Being upset with your mom because she talks down about you trying to go on a diet is understandable. As a member of your family she should be trying to be supportive of you rather than patronizing. Talk to her and maybe she'll understand that what she's doing isn't helpful.
I'm fine with her talking rude to me as long as I have the last laugh.
That's a toxic way to carry a relationship. You should seek to argue just to have the last laugh.