The twenty bucks you “forgot” to pay back tells your friend more than any birthday card.

Debts between friends are never really about the money. The amount is small enough that neither of you will mention it again, which is exactly what makes it such clear evidence: you knew, you could have, you did not, and they watched that happen. Affection gets measured in what you actually did, and a small debt is the cheapest place to check.

Pay back whatever is outstanding this week without being asked and without a story about why it was late. If it is genuinely tight, say the date you can do it and then do it on that date.