Decaf still has caffeine, just less. I have no idea on the safe level for cats, but don't assume decaf is safe. (I know this is a joke, but it needed to be said anyway.)
That is good to know, thank you. I didnt know this, good to be careful. I looked it up. 36 to 68 mg is fatal. So a couple sips isnt bad, but, being in a coffee shop it probably wouldn't be hard for Rocket to get enough to make him sick.
I'm actually not too sure how right you are here, my last cat was a chunky boy at 7kg, let's say that the upper end 68mg is the LD50, I'm roughly 70kg, 680mg of coffee would be very uncomfortable and unpleasant, but I don't think I'd be hitting the LD50.
LD50 in humans is probably around 100mg/kg, fatal doses are 150-200mg/kg