Vinegar is highly acidic and can cause gastrointestinal upset in cats, including vomiting and diarrhea.
It may also irritate their mouth and throat.
Suggestions
If you want to offer a small amount of vinegar to your cat, it should be heavily diluted with water.
However, it's best to avoid giving vinegar to cats altogether and opt for cat-safe treats instead.
Note: even if labeled as safe, any food can potentially cause allergies. When introducing a new food, please feed a small amount and observe your cat for any allergic reactions.