I thought this was funny because the “husband wolf” loves his shitty, lame joke so much, and the “wife wolf” looks exasperated with him. Fatphobia and sexism don’t even need be part of the equation. It’s okay to laugh!
While exercise is definitely a good thing, diet is the main factor for keeping a healthy weight. Kurzgesagt on youtube did a good video about it recently.
There are many lean people that eat absolute crap, and are as unhealthy or more. I don't think we make fun of bad eating habits; we make fun of fat people because they don't fit into certain beauty standards.
Also, being "fat" doesn't mean you're not healthy. Being a bit chubby or overweight is perfectly normal, obesity is a problem.
And I think calling people "lazy" for being fat says more about you than anything. Exercise isn't the most important factor on weight, eating habits are. Specifically, calorie intake.