This is my "attempt" to create a "lip biting" Lora.
I have to call it attempt, because I think, that this is really difficult to achieve with AI model.
Why?
Usually all AI Models are primarily trained with non-ugly images, which e.g. have the unspoken principle of symmetry in the face topology- the lip biting but has the aspect the "biting" is only done on one side of the lower lip.
For this reason some hints:

-Best results with Strength 1.6 - 2.0

-Positive prompt:
"(biting lip, lip bite, bitinglip:1.2), parted lips, teeth"

-Negative prompt:
"big mouth, (asymmetric eyes:0.5), symmetric mouth​​​"
(Background: the majority of the training images showed the mouth only and I think this leads to the tendency to enlarge the mouth unnaturally. On the symmetry thing I already made an explanation above)

-Don't apply a full face Adetailer or other face correction tool. Apply one for the eyes only but nothing which tries to correct the mouth as it will probably remove the lip biting