You shouldn't feel any guilt. They were terrible to guilt you into paying it forward. The entire concept is based on individuals choosing to do so and not a coffee shop insisting on it. I've done it and I've been on the receiving end and it is a fun thing to do. The time it happened to me I was financially strapped because of my divorce and it turned a terrible day around. But what this employee at the coffee shop did to you was terrible pressuring you with guilt and an inquisition. And $50 is a huge amount for a pay it forward coffee shop. You were meant to forget your wallet that day.