Better to avoid
Skip it. Avocado’s persin is mildly toxic to cats, the fat content upsets stomachs, and the pit is a hazard. Cats lose nothing by never tasting guacamole.
Cats are more sensitive than dogs to persin, the antifungal compound throughout the avocado plant, though far less than birds and rabbits, for whom avocado is deadly. In cats, realistic exposure (licks of flesh) usually means at most digestive upset — vomiting or diarrhoea — while the high fat content can trigger pancreatitis in susceptible individuals. Guacamole compounds the problem with onion and garlic. There’s no nutritional case for it: the “healthy fats” marketing applies to humans, not obligate carnivores.
None deliberately. A small stolen lick of plain avocado is unlikely to need more than observation in a healthy adult cat; anything more — or any guacamole — warrants a call to the vet.
For coat-friendly fats, ask your vet about fish-oil supplements made for cats; for treats, plain chicken.
Related: Can dogs eat avocado? · Can cats eat onions? · Can cats eat tuna?
This article is general information, not veterinary advice. If your pet has eaten something potentially harmful or shows symptoms, contact your vet or an emergency clinic immediately. Full disclaimer.