Is there a legal limit as to how fat you can become?

Well if they were gonna throw people in jail for being fat, I think they’d have to redesign the jail cells and facilities. They’d also have to make bigger jumpsuits. Being fat isn’t a crime. They can’t lock you up just for eating yourself to death. But most people over 500lbs or so are basically prisoners in their own homes. Most can’t walk, drive, or do anything on their own. They need help just to bathe or use the toilet. You should watch “my 600lb life” and see how sad their lives are. It’s actually really depressing. 

You die at right around a thousand pounds, so I guess that would be the limit. You don't go to jail cause they don't want to feed you!

I don’t know, but if there is then there should also be a legal limit for how stupid a question you can ask. Fair is fair.

You can legally become Jabba the Hutt

No, nor is there a biological one that we have seen.   Obesity is quite fascinating when you understand it.   

Quite the evolutionary marvel. 

It sounds like you're a little worried.  What are you up to now?