I think he is saying have an old card that you know will get declined

Try to use it to pay for dinner or at a bar or whatever

Then when they come back to tell you that your card is declined….

Tell them oh shit sorry ummm I left all my other methods of payment at home

All I have on me is this bitcoin, so if you wanna get paid for my bar tab or my meal then u better accept my sats

Weather it’s on chain or lightning doesn’t really matter…. I guess