How to refuse others to ask for business cards

When others ask for their own business card, but do not want to give it to each other, they should not be straightforward, but should express this idea in a euphemistic way. You can say "sorry, I forgot to bring my business card" or "sorry, I've run out of business cards.". However, if you are holding your business card in your hand and are seen by the other party, it is obviously inappropriate to say so.

If I don't have a business card and don't want to say it clearly, I can also use the above method to express it euphemistically.

If you don't have your business card or you've run out of it, you can say so, but don't forget to add the sentence "make it up some other day", and do what you say and do. Otherwise, they will be interpreted as having no business card, or deliberately not wanting to give each other a business card.