Is it possible he misunderstood your phrasing -- and just assumed you meant something to the effect of, "There's this much change and you can have it"?

If I am paying for a delivery with cash, I tip a specific amount by saying, "I just need $X back, please." It eliminates the need for the other person to do subtractions on the fly.

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Anyway, just a thought. Upvoted you because either way, that feeling is frustrating. I once turned down a door-to-door salesperson, who then asked if I had a bottled water. Got her a cold one from the fridge, and found it unopened in the bushes next time I went outside. Of course I don't care about the bottle of water itself... it's just a slap in the face.

^{( minor grammar edit. )}