when someine has a under bite to the absolute extreme, you than refer to that as a jimmy jaw.

ex. katie had such an under bite that everyone says she has a jimmy jaw.

"I'll be back from vacation soon. How are my fish doing?"
"Yeah, about that... 😅"

"He went to choke the chicken..."
"But that's animal abuse! How are you guys okay with this?!"
"I don't think that's what he meant by that 😅"