I'm going to poke fun at my wife for getting off her diet.
Why would you poke fun at her for that?
It's because she also made me gain weight.
It's not right to laugh at your wife for not sticking to her diet because she might feel bad about herself. You should be kind to her, and try to make her feel better about herself.
I'll do it anyway, she won't stop eating.
I think what you are doing is going to make her feel sad. You shouldn't care so much about what she eats.