My flatmate left some garlic butter out and I think I just caught my cat licking it.
He probably had about 3 "licks".
Is that a toxic amount? He is almost a year old.
It takes less than 1g of garlic per kg of body weight to harm a cat (it's about 5 times as potent as onion, which is a problem past 5g per kg). Your cat's 3 licks shouldn't have been enough -- you didn't say how much your cat weighed, but to be safe, I've set your cat's weight to be 8 lbs (~3.6 kg) for this. Your cat would have needed to ingest .008 lb of garlic, about 1 supermarket clove's worth. While dips are often more concentrated than standard, three licks shouldn't be a problem. If your cat seems lethargic and gets white gums in a few days, however, I'd take it to the vet.