One piece reaction

Luffy Kidd law React to their S/o eating his meat

Luffy

If Luffy's partner were to eat his meat, he would probably react excessively. I can see Luffy being taken aback at first, given his love of meat in particular. He might widen his eyes and make a playful exclamation to convey how shocked he is. However, Luffy wouldn't get upset or harbor resentment because he is a carefree and enjoyable person. Rather, he would probably find it funny and laugh it off; he might even join in on the joke by making light of his S/O. I'm sure Luffy would find this situation more entertaining than anything else because of his carefree attitude, which enables him to enjoy the small things in life and not take things too seriously.

Kidd

Kidd might react differently to his significant other eating his meat because he's a bit more serious and possessive about his possessions. He would most likely look surprised and perhaps a little irritated or annoyed. Given his reputation for guarding his possessions and personal space, Kidd may become defensive if he witnesses someone stealing his food.
But it's crucial to remember that every relationship is unique, and Kidd's response might be influenced by the dynamics between him and his significant other. Kidd may be more playful or teasing when expressing his displeasure than truly angry if they have a close relationship and mutual understanding. He could glare at them and say something like, "Hey, that belongs to me! The next time, you had better save some for me." Generally, depending on their relationship, Kidd's response would probably be a mixture of surprise, possessiveness, and maybe even humor.

Law

Given his laid-back and easygoing nature, Law would likely react more calmly if his partner started eating his meat. Though at first he might be taken aback, his reaction would probably be humorous and lighthearted.
Law would most likely chuckle and say something clever like, "Well, it appears that this person has good taste in food." Please remember to save some for me the next time. He would understand that sharing food is a normal part of a relationship, so he wouldn't get too upset about it. The fact that his significant other liked his meat enough to eat it without asking might even endear him to it.
But just like in any relationship, it's critical to keep lines of communication open and to honor one another's boundaries. Law might politely voice his concerns and ask that his S/O ask before consuming meat going forward if he has dietary restrictions or a special attachment to his food. Law would, however, probably respond in a humorous and understanding manner overall, highlighting the value of honest communication in their partnership.