Bacon — Food safety facts
Feed with care · Cats · full breakdown on the linked food page
Very high in salt and fat — a small crumb is okay, but regular feeding causes pancreatitis and obesity.
Short answer
A small lick is usually fine, but bacon grease is extremely high in fat and salt. Watch for vomiting, diarrhea, or unusual lethargy over the next day. Offer fresh water and call your own vet if you notice any of these signs.